Two proteases, assayed with fluorogenic peptides and tentatively designated Rcand Kc, have been isolated from nuclei of rat testis cells by differential extraction with acetic acid, removal of some proteins at pH 4.5, and polyacrylamide gel electrophoresis followed by electroblotting onto nitrocellulose paper. Protease R hydrolyzes t‐Butyl‐oxycarbonyl‐Val‐Pro‐Arg‐7‐amino‐4‐methyl‐coumarin and other peptides in which arginine is joined to 7‐amino‐4‐methyl‐coumarin by amide linkage. Protease Kchas a preference for peptides terminating in lysine‐7‐amino‐4‐methylcoumarin amide. Neither of these proteases is active against Glu‐Phe‐7‐amino‐4‐methyl‐coumarin amide or Carbobenzoxy‐Arg‐7‐amino‐4‐methyl‐coumarin. Proteases Rcand Kcpartially hydrolyze [3H] methyl ‐labeled histones H3 + H4 to trichloroacetic acid ‐ soluble peptides. Activities similar to proteases Rcand Kcare also found in cytoplas‐mic fractions of testis homogenates.