The Java mouse-deer is endothermic and homoeothermic, and has an average basal metabolic rate of about 4.883 watts. It also has the smallest red blood cells (erythrocytes) of any mammal, and about 12.8% of the cells have pits on them. The pits range in diameter from 68 to 390 nanometres. Red blood cells with pits are unique and have not been reported before either physiologically or pathologically.