Mice, were exposed to overpres ures of "long" duration in the expansion chamber of an air-driven shock tube inside which the initial, preblast pressures were varied over sixfold. When the animals were held at the initial pressure for one h-our following the bla-t before being returned to the ambient pressure of the laboratory, tolerance values, expressed as LDP0-1-hour gauge pressures, increased fourfold; they were 20.3, 31.0, 44.5, 55.4, and 91.8 psi for initial pressures of 7, 12, 18, 24, and

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... 42 psia, respectively. When animals were returned to ambient level soon after blast exposure, the LD press es were lower than the above values for initial pressures greater than ambient and higher for initial pressures lower than ambient. The~.easibility of scaling biological blast effects as a function of altitude-W" discussed and one approach suggested by available empirical data WvZs regarded as a promising, but tentative procedure. 4- ii j ACKNOWLEDGMENTS The able technical assistance of Mr.