Objective: The World Health Organization laboratory manual, last revised in 1992, states that the normal pH of semen ranges from 7.2 to 8.0. Our experience has been that values in our patient population are consistently higher than this range. To confirm this we reviewed >1100 semen records. Study Design: All patient records from January 1994 to December 1998 that had semen pH measurements and sperm concentration and motility measurements recorded were included in this study. We also determined the semen pH in a subgroup of patients who underwent sperm preparations for intrauterine inseminations that resulted in documented pregnancies. Histograms were used to describe the populations and the Mann-Whitney test was used for group comparisons. Results: For all patients (N = 1199) mean (±SD) semen pH was 8.2 ± 0.3. The range was 7.3 to 9.5, with pH <8.0 in 32% of the samples. The semen pH among the patients with normal sperm concentration and motility values (n = 602) was not different from that among those with abnormal parameters (n = 597). Mean semen pH value was 8.2 for both groups. In a small group of patients (n = 19) whose sperm preparations had been documented to result in a clinical pregnancy after intrauterine insemination the semen pH was 8.3 ± 0.3, with a range of 7.9 to 8.7. Conclusion: Our study questions the reference range defined by the World Health Organization for semen pH of 7.2 to 8.0. The mean values that we observed in our population, including those of samples from patients with normal sperm parameters, consistently lay outside that range. (Am J Obstet Gynecol 2000;182:1045-7.)