AbstractThe relative amounts of incorporation of [3H]lysine into various brain areas and segments of the spinal cord in adult Cebus and Rhesus monkeys were studied. One hour after subcutaneous injection of [3H]lysine, animals were sacrificed and the brain and spinal cord samples taken and processed for3H}lysine incorporation into protein (Lowry et al., 1951; Wells and Bernstein, 1976). Analysis revealed Marked differences in metabolism among brain areas within each species of monkey as well as across species. Cortical structures were generally higher in radioactive uptake than subcortical structures in both species. The Cebus monkey had the greatest variation among brain areas, particularly between cortical regions, whereas the Rhesus monkey did not show cortical variation in uptake. The ratio of incorporated to nonincorporated lysine in the brain and spinal cord was higher in the Rhesus than the Cebus monkey. Both species showed a rostrocaudal gradient of radioactivity following [3H]lysine incorporation into the spinal cord. Considering weight, size, and availability differences, the metabolism of [3H] lysine appears to differ by brain areas and spinal cord segments between species.