SUMMARYNutritional experiments were carried out dealing with : (1) the utilization of sulphur compounds; (2) the action of different mineral salts and their interaction. The results showed that the species of Pythium used grew well a t 28O buffered with Sorensen's salt to give an initial pH of 6-5 and incubated for 13 days for Pythium afertile and 10 days for the remaining species. Acid conditions below pH 5.0 and alkaline conditions above pH 8-0 were not tolerated. The best carbon and nitrogen sources are given. The best sulphur sources were Na,S, Na2S,0,, Na,SO,. 10 H20, Na,SO, . 7H20, Na,S,O,. 5H,O, K2S20a, molecular sulphur, m-methionhe, thioacetamide, L-cysteine, sodium thioglycolate, and DL-cystine Factorial experiments were carried out in which the fungi were incubated at 28' for 13-14 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, 10.0 g. 11. ; KC1, 0-5 gJ1. ; with varying amounts of K,HPO,, KNO, and MgSO, . 7H,Ofor the different species specified. There was a balance between K2HP0, and MgSO, . 7H20 for P. debarya w m and there were significant interactions between the salts above taken two at a time for P . debaryanurn and P . ultimum but the interactions for the remaining fungi were more variable. There was interaction between all three salts together for two of the species. P . debaryanum is more exacting in its nutritional requirements than the other species.Some species of Pythium are purely saprophytic, others are normally parasitic but may be saprophytic. Thus Pythium would seem to be a good genus for comparative nutritional studies. Previous work a t Newcastle upon Tyne (see Fothergill et al.) indicated that for some parasitic fungi the balance of the major inorganic salts in a culture medium was more important for the good growth of the mycelium than the concentration of individual salts, but in the case of some saprophytic species, the balance of salts was much less important. Results, however, over a range of fungi varied. The present experiments are a continuation of work designed to investigate these points. Excluding work done on Pythium as a plant pathogen, a few physiological investigations have been reported mainly dealing with the presence and function of pectinase in these fungi (