Cryopreservation of sperm is an important component of genetic conservation programs for fish.However, since fish eggs or embryos cannot be successfully cryopreserved and since the mitochondrialDNA is maternally inherited, the mitochondrial genomes of fish populations are presently not beingpreserved in these programs. One method of obtaining eggs from stored materials would be tocryopreserve embryonic cells that could later be transplanted into female recipient embryos, formingchimeras; a proportion of these transplanted cells would be expected to enter the germ line andsubscquently develop into eggs. The hypothesis of this study is that isolated blastomeres of rainbowtrout can be successfully cryopreserved and thawed. The objective of this investigation was to determine if the rate of cooling or the type of container alters cryopreservation success. Isolated blastomeres in a freezing solution containing 8.7% DMSO were subjected to one of two different cooling rates in either 0.5 ml French semen straws or cryovials. Thawed samples were examined using phase contrat microscopy, wkh cells scored as being either intact or non-intact. In the nonfrozen control group, 85.4%f 7.6 ($\bar{x}$ ± S.D.) of the blastomeres were intact. There was no significant difference between the cooling rates used in this investigation based on the proportion of intact cells, but there was a significant (p < 0.002) difference in the proportion of intact cells between samples frozen in French straws (35.9% ± 16.5) and those frozen in cryovials (19.4% ± 4.9).