Between 1963 and 1975, the annual suicide rate in England and Wales showed a sudden, unexpected decline from 5,714 to 3,693 at a time when suicides continued to increase in most other European countries. This appears to have been the result of the progressive removal of carbon monoxide from the public gas supply. In 1963, suicide by domestic gas accounted for 40 percent of suicides, but was virtually eliminated as a cause by 1975. These findings suggest that suicide is an intentional act chosen when moral restraints are weakened and when an individual has access to a means of death that is neither too difficult nor repugnant. This view has implications not only for the prevention of suicide, but for crime in general. That blocking opportunities, even for deeply motivated acts, does not result in displacement has not been so clearly shown before. The demonstration considerably strengthens the case for opportunity-reducing or situational means of crime control. 2 tables, 7 figures, and 105 references. (Author abstract modified)