Vesicular-arbuscular (VA) mycorrhizal fungi typically produce spores either within roots of a host plant or in the soil. Experiments were conducted to examine the effects of plant nutrition, as measured by tissue N, P, K, and soluble sugar concentrations, upon colonization of roots of Paspalum notatum Fliigge and sporulation within roots by Glomus intraradix Schenck & Smith and in the soil by Acaulospora longula Spain & Schenck and Gigaspora margarita Becker & Hall. Plants receiving a balanced nutrient solution without P consistently had the greatest percentage root length colonized by VA mycorrhizal fungi. Glomus intraradix produced more spores per root weight under conditions of nonmycotrophy, when plants received either water only or KH2PO4 only in the nutrient-poor soil used in these experiments. Gigaspora margarita and A. longula produced more spores in the soil when plants received the balanced nutrient solution without P. Similarly contrasting responses were seen when sporulation inside and outside the roots was correlated to plant nutrient and soluble sugar concentrations. The P-tolerant, intraradical-sporulating, VA mycorrhizal fungus G. intraradix sporulated heavily when N: P ratios of host tissue were imbalanced toward P. Acaulospora longula and G. margarita produced more spores in the soil when plant tissue N:P ratios were imbalanced toward N.