This note surveys the statistics of fire casualties classified as having been overcome by gas or smoke in the United Kingdom Fire Statistics for the years 1955–72 inclusive. For the period covered, the proportion of all annual casualties suffering from this source of injury (both fatally and non-fatally) has increased by a factor of about 3. Currently, about half the fatal casualties from all causes in fires per annum are overcome by gas or smoke. Possible reasons for this increase are discussed and, although the available statistics do not permit any causal relationships to be established, it is considered that major factors responsible are likely to have been an increase in the amounts and, perhaps, the irritancy of gas and smoke generated in fires, resulting in more persons being trapped. An examination of the proportion of casualties surviving exposure to smoke and fire gases shows no evidence of a significant change in the toxicity of fire gases.