In 3 laboratory experiments, mosquitoes were fed hepatitis C virus (HCV)-RNA positive blood by using membrane feeders, separated into head, thorax, and abdomen, and tested by a reverse transcriptase polymerase chain reaction for HCV-RNA. HCV did not replicate or disseminate in mosquitoes that had ingested blood from patients that were HCV-viremic positive. When yellow fever mosquitoes, Aedes aegypti (L.), were held for 1, 3, 7, 14, and 21 d after feeding, HCV-RNA was detected in the abdomens of 5/5 mosquitoes at 1 d after feeding; remaining tissues were negative with the exception of a single positive head at 7 d. In agreement, HCV-RNA was detected in Asian tiger mosquito, Aedes albopictus Skuse, and Anopheles stephensi Liston abdomens at 1 d, but not 3 d after feeding no HCV-RNA was detected in heads or thoraces. In addition, HCV-RNA was detected in heads of Ae. aegypti at 10 and 20 min, but not at 30 min, after feeding. The latter results raise the possibility of HCV contamination of mouthparts and, theoretically, mechanical transmission of this virus.