Chilling (-7.degree. C), heating (40.degree. C), and sonication were evaluated as methods of freeing oospores of P. megasperma var. sojae from viable mycelia. Hosts (Glycine max) were grown in soil infested with 1000 oospores/g (OPG) of soil from each treatment. Percentages of plants infected were 100, 100, 93 and 69 for untreated oospores, chilled, sonicated and heated, respectively. When chilled suspensions were used to infest soil at 0, 10, 100, 250, 500 and 1000 OPG, percentages of soybean seedlings infected were 0, 27, 65, 81, 98 and 100, respectively. Chilled oospores were evaluated for pathogenicity at 2-wk intervals 0-6 wk of storage. Relative root reduction of inoculated seedlings at 1000 OPG were 37.8, 30.8, 22.3 and 10.8 for 0, 2, 4 and 6 wk, respectively.