When blood cells of sixth-stage Prodenia eridania larvae were prevented from clumping by treatment with warm acetic acid vapors, fixation in hot water, or injection of nucleic acid, the number normally ranged from ca. 17,000 to 45,000, with a mean of about 28,000 per cu. mm. If clumping was not prevented, at least 38% of the cells were not available for estimation. Normal total hemocyte counts were found after injection of foreign material (trypan blue, India ink, and Bacillus subtilis), after starvation for 70 hours at 4° C, after ligaturing of the head or anus, and in grossly unhealthy larvae from moribund cultures. Starvation at room temperature led to desiccation of Prodenia larvae, and to a qualitative decrease in the blood volume, and therefore to an increase in number of cells per cu. mm. It is suggested, however, that the absolute number of cells in the animal remained the same. The number of blood cells was greatly reduced in larvae having a naturally occurring bacteremia. On the basis of these findings the blood cells of Prodenia eridania seemed not to constitute a particularly effective system for the defense of the organism.