Objectives. To test the study hypothesis that GPs participating in co-operatives will have more positive attitudes towards co-operatives, better mental health and less stress than GPs using traditional out-of-hours arrangements.Methods. A comparative questionnaire study was conducted amongst GPs, participating, or not, in an out-of-hours, largely rural, co-operative ('NoWDOC') which had been established one year previously. The general attitudes of GPs towards out-of-hours work were obtained together with responses to the General Health Questionnaire-12 (mental health) and Stress Arousal Checklist (job stress).Results. Eighty-nine of 120 eligible practitioners responded (74%). The mean GHQ scores for GPs in NoWDOC was 10.2 [standard deviation (SD) 3.9] compared to a score of 11.3 (SD 4.5) for those not participating (t = -1.18; P = 0.24). The overall mean stress score for members of NoWDOC was 3.8 (SD 2.6) compared to 3.4 (SD 2.7) for non-NoWDOC (t = 0.59; P = 0.55). The overall mean arousal score for NoWDOC GPs was 5.2 (SD 2.0) compared to 5.5 (SD 2.9) for non-NoWDOC GPs (t = -0.68; P = 0.50). Multiple regression analyses suggested that the independent variables (partnership arrangements, age, working hours and membership of NoWDOC) did not account for any of the variability in the GHQ score but a significant amount of variability in stress and arousal scores.Conclusions. The anticipated differences in mental health and job stress among participating GPs were not shown. As the new generation of GPs resemble the NoWDOC participants in their preferences for multi-partner practices with limited out-of-hours care provision, clarification of these findings is important.