The flow characteristics during zoospore release and cytoplasmic discharge from sporangia were studied in double-distilled water using severalPhytophthora species andPythium aphanidermatum. The time for passage of a zoospore through the exit pore increased and flow velocity decreased linearly with increasing volume of discharged cytoplasm fromPhytophthora sporangia (three-phase germination type) as well as fromPythium sporangia. The number of zoospores per sporangium averaged 31 (P. cactorum), 38 (P. palmivora), and 68 (P. cinnamoni); the mean passage time per zoospore was about 1.40, 0.90, and 0.50 seconds, and the mean flow velocity was about 13,20, and 29 μm per second for the three species, respectively. Sporangia produced in bean meal broth released zoospores with a higher velocity than sporangia produced in a chloride salt solution. The different flow rates could be correlated with the diameters of the exit pores of the sporangia and with turgor pressures at the beginning of cytoplasmic discharge. Zoospore release fromPhytophthora sporangia could be stopped completely by transferring sporangia into solutions of osmotic water potentials between −2.4 and −3.6 bar. Cytoplasmic discharge is explained using an osmotic pressure-flow model based on the equation of Hagen-Poiseuille.