Blastocysts from nulliparous, multiparous, superovulated, post-partum, and lactating rabbits were recovered five to nine days post-coitum ( p . c.), weighed, and dissected in order to obtain the blastocoelic fluid for analysis of glucose, lactic acid, and nitrogen. The largest daily percentage of increase in the volume of blastocoelic fluid occurred between five to six days p . c . , whereas, the largest absolute increase occurred between seven and eight days p . c . The weight of the blastocyst and trophoblast, and the volume of fluid was higher in the multiparous and post-partum does than in others. At eight days p. c., the concentration of glucose in the blastocoelic fluid reached a maximum comparable to the maternal blood level; subsequently a decline occurred. Lactic acid levels were similar to those of glucose. The amount of protein increased dramatically until seven days p. c. The amount of non-protein-N to total-N reached a peak at six days p . c., then declined. The chemical composition of blastocoelic fluid was influenced by the maternal condition, i. e., glucose and lactic acid were higher in superovulated (good response), overcrowded and multiparous groups than in others. While protein was lower in the overcrowded, post-partum and superovulated groups, it was higher in others.