Sixty cases of trichomonal vaginitis were randomly allocated to treatment with tinidazole or metronidazole, both administered as a 2 g single dose. One patient on tinidazole did not complete her follow-up. Parasitological cure was obtained in all patients in both the treatment groups. A satisfactory clinical response was obtained in all 29 patients on tinidazole, and in 27 out of 30 (90%) on metronidazole. Complete relief of sumptoms was obtained in 62% (18/29) and 13% (4/30) of patients ontinidazole and metronidazole, respectively (p less than 0.01). Ten patients on tinidazole and 24 on metronidazole manifested side-effects. The frequency and severity of side-effects were much more in the metronidazole group (p less than 0.01). Tinidazole has distinct advantages over metronidazole in the one-dose treatment of trichomonal vaginitis.