The impact of optimal temperature, osmotic pressure, and diet viscosity on the number of mosquitoes (Anopheles stephensi) feeding through a membrane, and on the size of the blood meal, was evaluated. An increase in diet viscosity decreased the number of imbibing mosquitoes, reduced the size of the ingested meal, and resulted in a slower rate of weight loss after feeding. The possible effect of these factors on the vectorial efficiency of mosquitoes is discussed.