ABSTRACT.A high level of sexual receptivity was displayed by females ofLucilia cuprina(Wied.) following the ingestion of a known amount of a standard preparation of a protein‐rich material (liver exudate), in addition to sucrose and water. A similarly high level of receptivity resulted from the ingestion of bovine serum albumin (BSA) plus a low molecular weight (MW) fraction of the liver exudate, or BSA plus an inorganic salt mixture, provided that the amount of BSA ingested equalled that of protein in the ingested exudate, the amount of low MW fraction was the same as that in the exudate, and the ingested salt mixture contained the same amounts of Na+, K+, Mg++and Ca++as were in this amount of low MW fraction. Substantial but less pronounced increases in receptivity followed the ingestion of equivalent amounts of BSA or low MW fraction alone. Receptivity was slightly increased by the ingestion of the inorganic salt mixture. When females were fed smaller quantitatively equivalent amounts of liver exudate or one or other of the two mixtures in the presence of low MW components, BSA was as effective, in inducing receptivity, as the high MW (protein) fraction of liver exudate, and the salt mixture was as effective as the low MW fraction when ingested together with protein. Receptivity correlated well with the mean ovarian developments of the groups of females which fed on the different materials. However, some lack of correlation at the level of individuals indicates that the control mechanisms for the two are at least partially distinc