A count was made of the number of engorged larvae and nymphs of Hyalomma (Hyalommasta) aegyptium (L.) which dropped each day from artificially exposed homiothermic vertebrates with different skin temperatures and from reptiles held at different constant temperatures. The daily larval drop from homiotherms, with skin temperatures between 32° and 400°C, showed no correlation between the engorgement period and skin temperature. With larvae on poikilotherms at 300°C and above there was also no relationship, but with nymphs a small correlation was apparent. Engorgement was particularly temperature sensitive between 20° and 30°C; for each drop of 1°C the larval and nymphal engorgement periods increased by 1-1/2 and 3-1/4 days respectively. The threshold temperature for complete engorgement was 20°C. At lower temperatures both subadult stages fed only occasionally and ultimately died before completing engorgement while still attached to the host. The ticks attached to hosts at temperatures down to about 10°C; at this temperature the ticks drew small amounts of fluid from the skin but apparently no blood. For the same temperature, the engorgement patterns were similar regardless of poikilothermic host species. Although H. aegyptium is usually a 3-host tick, it sometimes behaved as a 2-host tick on the Eurasian hedgehog (Erinaceus europaeus), laboratory rat, laboratory rabbit, Mediterranean gecko (Hemidactylus turcicus) and starred agama (Agama stellio), but not on the laboratory mouse, chicken, barn owl (Tyto alba), tortoise (Testudo kleinmalznni), chameleon (Chameleo chamaeleon), or lizard (Lacerta laevis). Some skinks (Eumeces schneiderii, Chalcides ocellatus) and snakes (Coluber numifer, Coluber rhodorachis, Rhynchocalamus melanocephalus) could not he infested with larvae either at room temperature or at 30°C.