In evaluating the host ranges of mosquitoes, 9 basic feeding patterns emerge. There are mosquito species that feed (1) almost entirely on mammals, e.g., anopheline mosquitoes, Culiseta inornata ; (2) almost entirely on birds, e.g., Culiseta melanura, Culex pens ; (3) readily on both birds and mammals, e.g., Culex pipiens quinquefasciatus ; (4) almost exclusively on amphibians, e.g., Culex territans ; (5) predominantly on reptiles but will take an occasional blood meal from a homeothermic animal, e.g., Deinocerites dyari ; (6) entirely on fish, e.g., Uranotaenia lateralis ; (7) readily on both poikilothermic and homeothermic animals, e.g., Deinocerites epitedeus ; (8) preferentially on birds in the spring and early summer with a shift to feeding on significant numbers of mammals in the mid and late summer periods, e.g., Culex tarsalis, Culex nigripalpus ; (9) almost exclusively on mammals in one geographic area and in another on birds, e.g., Culex erythrothorax . Of the several methods used for determination of host ranges, only advances in serologic technique are discussed in detail. The precipitin test, of which there are several variations currently in use, continues to be the basic serological tool for blood-meal identification. The passive hemagglutination inhibition (PHI) test offers promise as a practical method of distinguishing closely related host species. However, the PHI test is a more elaborate and difficult test when compared with the precipitin test.