Because salivary function and blood location are impaired in sporozoite-infected mosquitoes, we determined whether such pathology also could lead to an increased biting rate. For 5 days, we compared relative daily biting rates of Plasmodium gallinaceum sporozoite-infected mosquitoes (Aedes aegypti) and noninfected mosquitoes with an olfactometer. Mosquitoes then were exposed for 5 min to an anesthetized guinea pig. Infected mosquitoes exhibited a significant increase in olfactometer response which was also reflected in a decreased egg output. We conclude that if duration of contact with a host is limited, then infected mosquitoes may make more attempts at probing before being successful, and thus enhance transmission.