The effect of temp. on the longevity of the conidia of H. oryzae was investigated by storing small samples of conidia in screw cap vials at temps. ranging from 2-31 [degree]C. Viability was measured periodically by determining the % of conidia capable of germinating within 4 hrs. on potato-dextrose agar. After 100 days'' storage, 81% of the conidia stored at 2[degree]C were viable, while 6% of those stored at 31 [degree]C were viable. In expts. in which 5 temps. ranging from 10-31 [degree]C were employed and rel. humidities of 20, 45, 70, and 95% were provided by H2SO4 solns., the conidia retained their viability best when stored under cool dry conditions. The importance of rel. humidity was shown by the fact that at 20% rel. humidity the conidia survived for 6 months with little loss of viability even at 31[degree]C, whereas at 95% they failed to germinate after 1 month at 31[degree].