Alfalfa pellets and chicken lay mash were used to obtain polluted water for continuous and sustained oviposition by Culex mosquitoes. Water in fiberglass tubs enriched with 0.1 and 0.25 percent (w/v) of either material received heavy oviposition by gravid mosquitoes. The higher level of enrichment resulted in greater oviposition than lower concentrations which in turn received significantly more oviposition than the controls with no enrichment. Oviposition continued in the enriched tubs for more than 43 days where Culex quinquefasciatus and Culex stigmatosoma constituted a major proportion of the eggs laid while Culex tarsalis, as expected, oviposited at much lower rates than the other two species. Supplemental enrichment of mosquito breeding sources with organic material can thus provide uniform and sustained availability of some mosquito larvae for the evaluation of persistent control agents and other related studies.