We determined the Human Blood Index (HBI) of malaria mosquito vectors in Equatorial Guinea. We used a polymerase chain reaction (PCR)-based methodology to identify blood meal sources in engorged mosquitoes. We observed high HBI values, indicating that these vectors are highly anthropophilic despite intensive intradomicillary application of residual insecticides. Our results suggest that estimating the HBI can be a relatively simple and easy way to evaluate the efficacy of antimalaria interventions where an observed diversion to non-human hosts may successfully contribute to the interruption of malaria transmission.