A high scrotal temperature is a common finding in infertile patients and experimental studies indicate that specific types of heat exposure reduce semen quality. More and more men have a sedentary work position, which increases scrotal temperature. Semen and blood samples from 99 healthy men were analysed in relation to scrotal skin temperature obtained by a 24-h continuous monitoring protocol. Information on sedentary position at work and during spare time was collected by questionnaires. A negative correlation was found between high scrotal temperature and sperm output. Sperm concentration decreased 40% per 1 degrees C increment of median daytime scrotal temperature (95% CI: 8-71%). Similar results were found for total sperm count, FSH, and inhibin B. Motility, morphology, pH, and testosterone were not significantly associated with temperature. Only weak and inconsistent associations were found between sedentary position and semen quality. We conclude that scrotal temperature and semen quality are closely associated. Sedentary work position encountered in ordinary jobs, although a strong determinant of scrotal temperature, does not seem to have any effect on semen quality.