The effects of strain differences, irradiance level, photoperiod, and cell density on sexual reproduction were studied in the snow alga, Chloromonas chenangoensis, from Upstate New York. Mating experiments were conducted over an 8-hour period and normal, abnormal, and total matings were tabulated. Significantly more total matings were observed in strain CU 725B than in CU 721A, and consequently strain CU 725B was used in the remaining experiments. There were no significant differences in total matings among irradiance levels of 70, 85, 100, 115, 130, and 145 μmol photons m-2s-1 or cell densities of 0.5 × 106, 1.0 × 106, and 1.5 × 106 cells mL-1. When comparing photoperiods of 12: 12, 14: 10, 17: 7, 20: 4, and 24: 0 hour (light: dark), there were significantly more total matings in photoperiod 24: 0 than in 12: 12, but other differences were not observed. There were no significant differences in abnormal matings in any experiments and the percent of abnormal matings varied between 7-19%. Comparisons are made between this taxon and its close relative, Chloromonas tughillensis, with respect to optimal conditions for sexual reproduction.