Acute epididymitis: why patient and consort must be investigated. In this prospective study of 49 patients under 35 years of age with clinically diagnosed epididymitis, detailed microbiological investigation identified an infective cause in 67%. Chlamydia trachomatis was the commonest agent, present in 25 patients, but in 12 of these detection was based solely on raised antibody titres; 20 of the 28 female consorts screened were partners of men with chlamydial epididymitis and 80% of them were also positive for this infection. Isolating the micro-organism from 14 of 16 consorts indicated active infection despite the negative swabs from the men. If this important infection is to be adequately treated we recommend that all patients in this age group with epididymitis and their partners should be referred to a specialist unit with access to full chlamydia laboratory facilities. 