A series of three experiments were carried out. A total of 204 dogs and 115 goats were exposed to shock-tube and high-explosive-produced reflected shock waves ranging in duration from 400 to 1.5 msec. LD50 values, calculated by probit analysis, showed similar patterns for both species, increasing at the shorter duration by a factor of 4 or 5 above those for long durations. Sixty dogs were exposed in a shock tube to "sharp"-rising overpressures of near of 400-msec duration at six-dose levels ranging form 9.2 to 35.8 psi. The degree of lung injury was graded and threshold for petechial hemorrhage determined. Dose-response curves were compiled using data for 200 mice, 110 hamsters, 150 rats, 120 guinea pigs, 48 cats, and 40 rabbits exposed to "long"-duration reflected pressures in a shock tube. The tolerances (LD50) for all six species are compared. Pathological observations for all species and lung-weight data for cats and hamsters are included. Criteria for relating biological response to various parameters of the blast wave are discussed.