Studies were conducted to determine optimum replacement intervals, storage times, and vertebrate source of blood used to feed Haematobia irritans (L.) adults in vitro. Feeding success was measured by the total number of larvae produced per female during 10-d experimental periods which combined adult female survival, egg production, and egg hatch. The number of larvae per female was reduced significantly when blood replacement intervals were increased from 24 to 48 h; however, blood replacement intervals could be increased to 48 h without affecting larval production if the blood was agitated continuously. Maximum larval production was obtained when adult flies fed on whole, citrated bovine blood that had been stored at 3 degrees C for 2 wk; however, there was no difference in the number of larvae produced per female when adults were fed blood stored at -20 degrees C for 2-52 wk. Significantly more larvae were produced when adults fed on citrated porcine blood than bovine or ovine blood.