The susceptibility of Aedes vexans, Culex quinquefasciatus, and Culex tarsalis to Dirofilaria immitis infections was evaluated in Bernalillo Co., New Mexico. Mosquitoes that had taken a blood meal from a D. immitis-infected dog were dissected and observed for developing larvae. Infection rates for Ae. vexans, Cx. quinquefasciatus, and Cx. tarsalis were 68.9, 40.6, and 30.2%, respectively. Infective D. immitis larvae developed after a minimum of 8 days in Ae. vexans vs. 14 days in both Cx. quinquefasciatus and Cx. tarsalis. Vector efficiency of Ae. vexans was 20.4%, with a mean of 5.9 infective larvae developing from a mean of 29 microfilariae ingested per mosquito. Vector efficiency in Cx. quinquefasciatus and Cx. tarsalis was 2.7 and 0.4%, respectively. These results suggest that Ae. vexans has the greatest potential for D. immitis transmission.