Incorporation of³H-inositol and³²P into the mycelium ofTrichoderma viride shows that this fungus contains phosphoinositides (PI) and inositol phosphates (IP). Under conditions suitable for the induction of photoconidiation, a pulse of light did not elicit a change in the incorporation of³²P but decreased the incorporation of³H-inositol into PI. The incorporation of³H-inositol into IP was unaffected by light. Inhibitors of PI metabolism, Li⁺ and neomycin, inhibited more effectively photoconidiation than vegetative growth. The distribution of the³H-inositol label in inositol phosphates was not changed by the light pulse.