SUMMARY: Fatty acids are required for the growth of Pityrosporum ovale (Bizzozero) Castellani et Chalmers; myristate or palmitate satisfies this requirement. Oleate increases the crop of organism in a medium containing limiting concentrations of myristate or palmitate. When [1-14C]-myristate was added to the medium the cells of P. ovale contained myristate, palmitate, stearate, oleate and linoleate with approximately the same molar specific radioactivity as myristate. Thus P. ovale can synthesize both saturated and unsaturated fatty acids of higher molecular weight from myristate.