The purpose of this study was twofold. In the first part are compared cryosurvival rates for human semen following two different freezing and three different thawing techniques. In the second part a larger number of samples processed by the best of the six methods described were examined to ensure reproducibility. Eighteen human semen samples with initial motility greater than 60% and density greater than 20 X 10(6)/ml were mixed with a cryopreservative medium at 35 degree C and vacuumed into 0.5 ml straws. Six aliquots were prepared from as many specimens as possible. Three straws were frozen by a programmed method (P) and three by a rapid freezing technique (V). All six straws were stored in liquid nitrogen vapor (-196 degree C) for 1 week. The straws were thawed by 1 of 3 methods: (1) room temperature for 10 minutes and 37 degree C hot plate for 10 minutes, (2) ice water for 10 minutes and 37 degree C hot plate for 10 minutes, (3) 35 degree C water for 12 seconds and 37 degree C hot plate for 10 minutes. Postthaw motility was assessed for each aliquot. The freeze/thaw method P/1 was judged optimal. In the second part of the study a larger number of samples were processed by P/1. The mean +/- standard deviation postthaw motility o 57 semen specimens processed by this method was 61.4 +/- 12.1.