['To determine the acceptability of an emergency medical dispatch (EMD) system to people who call 999 to request an ambulance.', 'Postal questionnaires to two systematic random samples of approximately 500 named callers to one ambulance service before, and one year after, the introduction of EMD.', "The response rate was 72% (355 of 493) before, and 63% (297 of 466) after, EMD. There was a reduction, from 81% (284 of 349) to 70% (200 of 286), in the proportion of callers who found all the questions asked by the call taker relevant, although this did not adversely affect the proportion of callers who were very satisfied with the 999 call, which increased from 78% (268 of 345) to 86% (247 of 287). The proportion of callers who reported receiving first aid advice increased from 7% (23 of 323) to 43% (117 of 272) and general information from 13% (41 of 315) to 58% (157 of 269). Satisfaction levels with the amount of advice given increased, while satisfaction with response times remained stable at 76% (254 of 320) very satisfied before and 78% (217 of 279) after EMD. The proportion of respondents very satisfied with the service in general increased from 71% (238 of 336) to 79% (220 of 277). There was evidence in respondents' written comments of two potential problems with EMD from the caller's viewpoint. Firstly, some callers were advised to take actions that were subsequently not needed; secondly, a small number of callers felt that the ambulance crew did not treat the situation as seriously as they would have liked."] Do the acceptability of an emergency medical dispatch system to people who call 999 to request an ambulance?