Hematological values and diameters of erythrocytes are reported for bats from Colombia, Puerto Rico, and St. Croix. A marked variation was observed in most of the blood characters considered. Smaller bodied species had lower leucocyte counts than larger ones, as did non-gravid females and adult males when compared with pregnant and lactating females. Erythrocyte counts of frugivorous species were lower than those reported for insectivorous bats. Mean erythrocyte diameters were similar and had comparable ranges of variation. There were no significant differences between lactating, gravid, or non-gravid females in hemoglobin concentration, hematocrits, differential counts, or diameter of erythrocytes. Certain abnormalities in the blood picture were observed, and data are discussed in comparison with those obtained by others.