The levels of albumin, IgG, IgM, and complement (C3) were determined by enzyme-linked immunosorbent assay in Aedes albopictus and Phlebotomus papatasi at regular intervals after feeding on human blood. Albumin disappeared most rapidly; by 48 hr, detectable levels of albumin had decreased 100-fold. In contract, IgG and IgM survived longer and were still detectable at low levels several days after ingestion. C3 was intermediate in its rate of degradation. In general, serum protein disappearance occurred more rapidly in Ae. albopictus than in Ph. papatasi, despite a larger volume of blood ingested by the former.