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A series of experiments were conducted to determine the sensitivity of radish to four light alcohols (ethanol, methanol, 2-propanol, and t-butanol) identified as atmospheric contaminants on manned spacecraft. Radish (Raphanus sativus L. `Cherry Bomb' Hybrid II) seedlings were exposed for 5 days to concentrations of 0, 50, 100, 175, 250, and 500 ppm of each alcohol and the effect on seedling growth was used to establish preliminary threshold response values. Results show a general response-pattern for the four alcohol exposures at threshold responses of 10% (T10), 50% (T50) and 90% (T90) reduction in seedling length. There were differences in the response of seedlings to the four alcohols, with the T10 for t-butanol and ethanol (25 to 40 ppm) being 3 to 5× lower than for methanol or 2-propanol (110 to 120 ppm). Ethanol and t-butanol exhibited similar T50 values (150 to 160 ppm). In contrast, T50 for methanol (285 ppm) and 2-propanol (260 ppm) were about 100 ppm higher than for ethanol or t-butanol. Chronic exposures to 400 ppm t-butanol, ethanol or 2-propanol were highly toxic to the plants. Radish was more tolerant of methanol, with T90 of 465 ppm. Seeds did not germinate at the 500 ppm treatment of t-butanol, 2-propanol, or ethanol. There were significant differences in projected performance of plants in different environments, dependent upon the regulatory guidelines used. The use of exposure guidelines for humans is not applicable to plant systems.