The chemotactic activity of urethral exudate and the effect of treatment were assessed in 67 patients with nongonococcal urethritis (NGU) or gonorrhea. All samples demonstrated chemotactic activity related to the number of neutrophils seen on Gram's staining of the urethral smear. Chemotactic activity decreased after treatment in patients with Chlamydia-positive NGU (mean +/- SE, 21.1 +/- 2.7 cells/high-power field [hpf] before treatment; 8.7 +/- 2.2 after treatment; P < .004) and gonorrhea (25.6 +/- 5.2 cells/hpf before treatment; 1.6 +/- 0.7 after treatment; P < .015). Chemotactic activity increased again in Chlamydia-positive NGU patients to 21.0 +/- 3.3 cells/hpf (P < .05) 2-3 weeks after cessation of therapy in the absence of demonstrable infection or further intercourse. There was no significant decrease in chemotactic activity after therapy in the Chlamydia-negative NGU or persistent urethritis groups. These data suggest a previously unrecognized persistent chemotactic stimulus in urethral exudate from patients with urethritis.