Ridge gourd pollen has a stimulatory effect on the germination ofPseudoperonospora cubensis. The rate and percentage germination of zoospores increased in the presence of pollen leachates. Spraying of leaves with a mixture of pollen and sporangial suspension enhanced the development of lesions. Early germination of zoospores in the presence of pollen proved advantageous for infection as it provided a prolonged favourable infection period. The results are discussed in relation to the epiphytoties of the disease during flowering period.