Chlamydia trachomatis infections might have a detrimental effect on various sperm functions. Data concerning the effect of C. trachomatis on the capacitation activity of sperms are lacking. The study was undertaken to evaluate whether chlamydial infection influences acromsome reaction (AR). Three groups of men were investigated for ARs -Chlamydia negative (n = 46) and positive (n = 30) patients, and healthy men (n = 53) undergoing vasectomy. The fluorescence technique for the evaluation of AR was applied. The normal range for the induction of AR was assumed DeltaAR > 12.5% for this technique. Seminal plasma was examined for IgA antibodies against C. trachomatis. There was a significant difference in AR between healthy volunteers, Chlamydia-negative and Chlamydia-positive patients. DeltaARs were 15.8 +/- 1.6% in healthy volunteers versus 12.15 +/- 2.4% in Chlamydia-negative and 9.08 +/- 1.8% in Chlamydia-postive patients, respectively (P < 0.05). Significant elevated titres of C. trachomatis-specific IgA in seminal plasma showed a negative correlation with the AR of spermatozoa. AR seems to be a valuable marker, especially in couples with idiopathic infertility.