Infection from Chlamydia trachomatis (CT) in men with non gonococcal urethritis (NGU) and in women with cervicitis has been investigated by means of Chlamidiazime and serological tests. 32.5% of 120 men with NGU and 8.3% of 12 men with dysuria were positive to Chlamydiazine test. Serological test using anti-CT IgG antibodies gave positive results in 30% of men with NGU and 33.3% of men with dysuria. Positivity to higher-levels (1:64) of anti-CT IgG antibodies were demonstrated in 14.1% of NGU patients and 16.6% of men affected by dysuria. Of 11 women positive to Chlamydiazine test, 8 were affected by cervicitis and 3 had no symptoms. All female partners of Chlamydiazine-positive men with NGU resulted positive to Chlamydiazime test. Serological tests were more frequently positive in asymptomatic partners of men with NGU. These results give further evidence for the aetiological role of CT, and suggest that antigen detection assay is more sensitive in men with NGU and in women with symptomatic cervicitis. On the other hand, serological tests seem more useful in men with dysuria and in asymptomatic women.