Because Pinus ponderosa (Dougl.ex Laws) and P. radiata (D.Don) have exceptionally fast growth rates and their abscised needles are not readily dispersed by wind, these species may be valuable for removing radioisotopes from contaminated soils. P. ponderosa and P. radiata seedlings were tested for their ability to accumulate Cesium 137 and Strontium 90--characteristic radioisotopes of nuclear fallout--from contaminated soil. All seedlings were grown for 3 months in cu cm of sphagnum peat moss:perlite (1:1 V:V) in a growth chamber. In experiment 1, seedling accumulation of 137 CS and 90 Sr after 1 month of exposure was measured. In experiment 2, seedling accumulation of the radioisotopes during different-length exposures was measured. Experiment 3 measured seedling accumulation of CS 137 and SR 90 at different concentrations of the radioisotopes in the growth medium. Accumulation of CS 137 and SR 90 by both species increased with increasing concentration in the growth medium and correlated curvilinearly with radioisotope concentration in the growth medium. (Copyright (c) 1993, Environmental Quality.)