In 1990, microbiological ejaculate analyses were carried out on a routine basis on 125 andrological patients, in addition to the determination of the concentration, motility and morphology of the spermatozoa. Fourteen patients (11.2%) with therapy-requiring asymptomatic infections (TAI) > 10(4) CFU (colony-forming units) ml-1 were effectively treated with Ofloxacin (Tarivid) at 2 x 200 mg d-1 for a period of 20 d. Concentration, motility and morphology of the spermatozoa were determined before the Ofloxacin treatment and controlled 1, 3, and 6 months later and correlated to the values obtained before the treatment. Over the entire period of observation, the morphology did not change significantly, whilst initially 1 month after the treatment the concentration and the motility decreased significantly (P < 0.05). Three months later they again reached the starting values. After 6 months, a significant improvement occurred with regard to the motility, as compared to the starting values (P < 0.01), whilst the concentration remained at the level of the starting values. By this, Ofloxacin has been proved to be an effective medication for the treatment of TAI. In the end, it still remains an open question whether the improvement in sperm motility is primarily related to the Ofloxacin therapy.