Abstract Equations to predict site index, merchantable cubic foot volume, basal area, and average tree diameter were developed for unthinned Japanese larch plantations in Pennsylvania. The yield function indicates that a biological rotation of less than 30 years is reasonable on good sites. The findings are applicable to Japanese larch planted on old-field, abandoned farmlands, and cutover sites in Pennsylvania. North. J. Appl. For. 6:78-81, June 1989.