2-Bromopropane and hydrochlorofluorocarbons (HCFCs), whose toxicity has scarcely been known, have recently been introduced as main substitutes for chlorofluorocarbons (CFCs). A major corporation in Korea replaced CFCs with 2-bromopropane and this actually led 23 Korean workers to be the world's first 2-bromopropane intoxication victims. Out of 25 female workers in the tactile switch assembling section, 17 (68%) were diagnosed as having ovarian failure. Two affected female workers showed marked pancytopenia with markedly hypoplastic marrow. In the same section, two out of eight male workers showed azoospermia and four some degree of oligospermia. The above toxicity of 2-bromopropane was reproduced in experimental animal studies. Recently, health effects of HCFC 123, including toxic hepatitis, have been reported by several authors. The principle of replacement of toxic substances with non-toxic or less toxic chemicals is important in risk management, but substances still poorly known should not be confused with non-toxic or less toxic substances. Measures aimed at reducing exposure to chemicals with known toxicity rather than using new unknown alternatives may be a rational and effective approach to risk management.