The clinicopathological effects of x-rays, mechlorethamine hydrochioride (HN/sub 2/. HCl), triethylenemelamine (TEM), busulfan (Myleran), and 4M20 were studied in young adult mice of the RF/Up and (101 X C3H)F/sub 1//Cum strains. The LD/sub 50//30 days of these agents were as follows: x rays, 613 r; mechlorethamine hydrochloride, 0.127 mg per mouse; TEM, 0.073 mg per mouse; busulfan, 1.01 mg per mouse; 4M20, 4.41 mg per mouse. The mean time of death varied with the agent and dose; at the LD/sub 50//30 day level it was 13.0 days after x rays, 12.4 days after busulfan, 6.9 days after mechiorethamine, 5.9 days after TEM, and 3.5 days after 4M20. The predominant sites of injury varied with the agent as follows: x rays, hematopoietic organs and gonads; busulfan, hematopoietic organs, gastrointestinal tract, gonads; mechiorethamine, brain, hematopoietic organs, gastrointestinal tract, and gonads; TEM, hem atopoietic organs, gastrointestinal tract, and gonads; 4M20, liver, hematopoietic organs, and gonads. Injury to the brain by mechlorethamine and to the liver by 4M20 were effects peculiar to these two agents. Pretreatment of the mice with AET reduced the severity of injury to some organs more » from x rays and mechlorethamine but did not detectably alter the injury resulting from TEM. Paradoxically, AET pretreatment increased the severity of injury by 4M20 in the intestine and bone marrow. (auth) « less