SUMMARYNutritional experiments were carried out dealing with : (1) the utilization of sulphur compounds; (2) the utilization of phosphorus compounds; (3) the action of different mineral salts and their interaction. The results showed that Phytophthora erythroseptica grew well at 28" and pH 6-6 incubated for 20 days; P . parasitica grew well at 28' and pH 6.6 for 17 days; and P . infestans at 20' and pH 4.5 for 16 days. In the adjusted controlled medium pH changes were generally within one pH unit. The best carbon and nitrogen sources are stated. The only satisfactory sulphur sources for P . infestans were sodium sulphate and sodium thiosulphate. These compounds were also among the best S sources for P . erythroseptica and P . parasitica, but a number of other compounds also were utilized equally well, e.g. sodium metabisulphite, sodium sulphite, a-cysteine, sodium sulphide, sodium dithionite and methionine. For all organisms the best phosphorus sources were sodium dihydrogen orthophosphate, sodium metaphosphate and lecithin. Rate of utilization of the phosphorus was an important factor in mycelial yield. Factorial experiments were carried out in which P. erythroseptica and P . parasitica were incubated a t 28" for 17 days. Statistical analysis of the results showed that under the given conditions optimal growth measured as mg. dry wt. was obtained in liquid media containing glucose, 25 g./l. ; DL-asparagine, 4.0 g./l. ; FeSO, . 7H20, 0.001 g./L ; thiamine, 0.8 mg./I. ; ZnSO,. 7H20, 1 p.p.m. ; H2Mo04, CuSO, . 5H20, 0.02 p.p.m. ; with varying amounts of K2HP0,, MgSO,. 7H20 and CaS0,.2H20 for the different species specified. There was a balance between all combinations of K2HP0,, MgSO,. 7H20 and CaSO,. 2H20 for P . parasitica but not for P . erythroseptica, but there were significant interactions between the salts taken two at a time for both these fungi. There was interaction for all three salts together for both species. Phytophthora infestans and P . parasitica are more exacting in their nutritional requirements than P . erythroseptica.