A detailed analysis of suicide rates between 1960 and 1971 for England and Wales and for Scotland confirms that all age-sex subgroups have shown a marked decline in suicide due to domestic gas, corresponding in time to the fall in the CO content. After considering data on the effects of the International Classification of Diseases (ICD) Eighth Revision, accident mortality, some personal characteristics of coal gas suicides, and the use of coal gas in parasuicide it was concluded that a simple casual explantation was likely. Suicide due to non-gas methods has in general increased, markedly so in some groups. It was suggested that neither improved psychiatric services nor voluntary agencies could have produced such changes. The 'compensatory' trend of gas and non-gas suicide rates was indicated for certain age-sex subgroups. The continuing need for suicide research was pointed out, and questions were raised concerning the psychological meaning of the epidemiological data.