We developed a set of equations to estimate biomass of black spruce (Piceamariana (Mill.) B.S.P.), based on data from trees from bogs in Minnesota. The equation for total biomass, based on diameter alone, was similar to most other equations for black spruce in the literature. This relationship appears to have wide generality. Estimates of foliage biomass, arrived at by using the same tree diameter and height but various equations from the literature, differed greatly. These comparisons indicate that stand conditions, such as stocking, are apparently very important in determining mass of black spruce foliage.