Abstract
Human chromosomes from cultures of peripheral lymphocytes were prepared for electron microscopy by surface spreading and critical-point drying. Total and partial determinations of chromosomal dry mass were made from contrast in electron microscopic negatives. The distribution of dry weights was analyzed with respect to the Denver-Chicago classifications. There is considerable variability of mass within each group, but no statistically significant differences between four donors. A single chromosome can be correctly classified from its total mass and the ratio of long- to short-arm mass.