Inclusion Criteria for hypogonadal subjects:

• men with primary or secondary hypogonadism and testosterone serum levels below 300 ng/dl [= 10.4 nmol/l], on two occasions within a period of one month before inclusion;
• age: 20-60 years;
• normal thyroid function, physiologic prolactin concentration;
• normal otorhinolaryngologic examination (ENT examination);
• normal 24-h activity-rest pattern;
• written Informed Consent.

Exclusion Criteria for hypogonadal subjects:

• significant intercurrent disease of any type, in particular liver, kidney or heart disease, any form of diabetes mellitus or psychiatric illness (patients with treated hyperlipidemia, arterial hypertension or treated hyper- or hypothyroidism will not be excluded provided they have been stable on their medication for at least two months);
• history of, or current nasal disorders (e.g. seasonal or perennial allergic rhinitis, atrophic rhinitis, polyposis, abuse of nasal decongestants, clinically relevant nasal septum deviation, recurrent epistaxis) or sleep apnea;
• sleeping disorders;
• abnormal prostate examination indicative for prostate cancer or elevated serum PSA levels (PSA < 2.5 ng/ml for subjects < 40 years of age and < 4 ng/ml for subjects >= 40 years of age);
• history of cancer, especially breast, prostate or testicular tumor; excluding skin cancer;
• history of severe or multiple allergies, severe adverse drug reaction or leucopenia. A known hypersensitivity to lignocaine/lidocaine or all surgical dressings which may be used in the study procedures;
• history of abnormal bleeding tendencies or thrombophlebitis unrelated to venepuncture or intravenous cannulation, or a history of Hepatitis B, a positive test for Hepatitis B surface antigen, a history of Hepatitis C, a positive test for Hepatitis C antibody, a history of HIV infection or demonstration of HIV antibodies;
• the patient is a heavy smoker currently smoking > 20 cigarettes per day or smoking history >10 pack years (1 pack year is defined as 20 cigarettes per day for 1 year);
• regular drinkers of more than four (4) units of alcohol daily (1 unit = 300 ml of beer, 1 glass of wine, 1 measure of spirit) or those who may have difficulty in abstaining from alcohol during the 48 hours prior to the initial-dose administration and for the duration of the study;
• history or current evidence of abuse of alcohol or any drug substance, licit or illicit; or positive urine drug and alcohol screen for drugs of abuse and alcohol;
• treatment with other androgens (e.g. DHEA), anabolic steroids or other sex hormones within one month prior to Day 1 of the study;
• testosterone treatment in the previous 2 weeks (oral, buccal, topical, nasal) or 4 weeks (intramuscular);
• current or recent (previous 4 weeks) use of over the counter male enhancement products;
• use of nasal decongestants and nasal corticosteroids;
• shift work;
• transmeridian flights within 1 month before Day 1 of the study;
• poor compliers or those unlikely to attend;
• intake of any drug as part of a research study within 30 days of initial-dose administration in this study and throughout the study;
• blood donation within the 12-week period before the initial study dose.

Inclusion criteria for eugonadal subjects:

• men with testosterone serum levels above 300 ng/dl [= 10.4 nmol/l] on two occasions within a period of one month before inclusion;
• age: 20-60 years;
• normal thyroid function, physiologic prolactin concentration;
• normal 24-h activity-rest pattern;
• written Informed Consent.

Exclusion criteria for eugonadal subjects:

• significant intercurrent disease of any type, in particular liver, kidney or heart disease, any form of diabetes mellitus or psychiatric illness (patients with treated hyperlipidemia, arterial hypertension or treated hyper- or hypothyroidism will not be excluded provided they have been stable on their medication for at least two months);
• history of hypogonadism;
• sleeping disorders;
• treatment with other androgens (e.g. DHEA), anabolic steroids or other sex hormones within one month prior to Day 1 of the study;
• testosterone treatment in the previous 2 weeks (oral, buccal, topical, nasal) or 4 weeks (intramuscular);
• current or recent (previous 4 weeks) use of over the counter male enhancement products;
• shift work;
• transmeridian flights within 1 month before Day 1 of the study;
• the patient is a heavy smoker currently smoking > 20 cigarettes per day or smoking history >10 pack years (1 pack year is defined as 20 cigarettes per day for 1 year);
• regular drinkers of more than four (4) units of alcohol daily (1 unit = 300 ml of beer, 1 glass of wine, 1 measure of spirit) or those who may have difficulty in abstaining from alcohol during the 48 hours prior to the 24-h blood sampling day;
• blood donation within the 12-week period before the 24-h blood sampling day.