Dictyostelium cells when treated with 100 ppm carbaryl or placed on 20 ppm carbaryl agar showed profound changes in the developmental stages. The treated cells showed larger aggregate formations, inhibition of cAMP-chemotaxis and cAMP dependent extracellular phosphodiesterase activity. The fruiting body formations were also scarce. The developing Dictyostelium cells when placed on carbaryl agar showed aberrant morphogenesis with larger aggregates, abnormal slugs and large fruiting bodies. In all cases the development of the treated cells showed considerable delay when compared with controls.