In this study 66 male patients with erectile dysfunction were investigated. The authors measured the testosterone levels in serum and in saliva, which latter represent with good accuracy the serum levels of free testosterone. The mean serum total testosterone level was 17.6 nmol/L (confidence intervals: 15.5 and 20.2 nmol/L, normal range: 10-50 nmol/L). The mean salivary free testosterone level was 218.5 pmol/L (confidence intervals: 198.3 and 239.9 pmol/L, normal range: 200-1000 pmol/L). Low salivary (free) testosterone levels were found in 36.4% of patients, while only in 10.6% of patients had low serum testosterone levels (p = 0.01, by binomial test). Although there is a relationship between serum and salivary testosterone levels (r = 0.41, p < 0.001), the patients with low salivary (free) testosterone levels have in major part a normal serum total testosterone level. These data indicate that a considerable proportion of patients with erectile dysfunction have androgen deficiency. The serum total testosterone level is not a sensitive indicator to detection of hypogonadism. The androgen substitution therapy has a beneficial effect on erectile dysfunction in a significant part of patients. The measurement of free testosterone level in saliva may have an important role both in the diagnosis of diseases characterized by androgen deficiency and hyperandrogenic status.