An outbreak of a geometrid moth, Stamnodes animata (Pearsall), in northwestern Nevada defoliated approximately 4,000 ha of curlleaf mountain mahogany during 1978 and 1979. To determine the potential importance of accelerated nutrient release to developing understory vegetation, we measured total organic nitrogen (TN), phosphorus (TP), and sulphur (TS) in the surface 1 cm of litter, total litter layer, and upper 3 cm of soil; and availabilities of nitrogen (N), phosphorus (P), and sulphur (S) in the surface 4 cm of soil under defoliated and nondefoliated trees. Two years after onset of the looper outbreak, defoliation caused no detectable change in concentrations of TN, TP, or TS in surface litter, the total litter horizon, or upper 3 cm of mineral soil. The most striking effect of the infestation was a significant 1,186 g/m² increase in litter weight under defoliated trees resulting in an additional 18.8 g/m² of TN and 0.9 g/m² of TP and TS in the litter layer under defoliated trees. Input comprised 4.5 to 6.4 percent of the total capitals of TN, TP, and TS in the litter layer and surface 3 cm of soil. Availability of N or P in soil did not differ between defoliated and nondefoliated trees, but S was significantly more available in soil beneath nondefoliated trees. Because of the already high levels and availabilities of N, P, and S in surface soils beneath Cercocarpus trees, responses of understory vegetation to looper defoliation would likely result primarily from increased light and moisture. Forest Sci. 31:382-388.