Two insect growth regulators, namely CME 134 and Dowco 439, have been tested for their effect on growth and on aflatoxin B1and lipid productivity inAspergillus flavus.No effect on growth and lipid production was detected. However, various concentrations of CME 134 and Dowco 439 showed significant inhibitory effects on aflatoxin B1production. The degree of inhibition was dependent on the concentration and time of application. Inhibition was observed when Dowco 439 was added at inoculation and again 3, 6, 9, 12 and 15 days after inoculation, as well as after the addition of either CME 134 or Dowco 439 to the individual cultures at inoculation and 3 days after inoculation. However, the addition of either CME 134 or Dowco 439 as late as 6 days after inoculation markedly decreased the inhibition of aflatoxin B1production.