In a retrospective study 84 patients aged > or = 50 years undergoing emergency appendicectomy were matched for age and sex with 84 randomly selected emergency admissions as controls. Of the former, 31 (37 per cent) were taking non-steroidal anti-inflammatory drugs. (NSAIDs) at admission, compared with nine (11 per cent) of the controls (P < 0.01). In the study group a suppression of the white cell count was identified on admission in those taking NSAIDs (mean 11.9 x 10(9) l-1) compared with those not (mean 14.8 x 10(9) l-1) (P = 0.007). This is the first reported association between appendicitis and NSAIDs. The relative risk by odds ratio was substantially increased at 6.5 (95 per cent confidence interval 2.1-8.8). An NSAID-related impairment of host defences leading to failure in the resolution of inflammatory episodes may explain this association. It is further postulated that the suppression of the white cell response may be a marker of such an effect.