OBJECTIVES: To assess preference and willingness-to-pay (WTP) for the insulin mixture Humalog Mix25 relative to Humulin 30/70, from the perspective of patients in five European countries. The relative value of individual treatment attributes was also determined. METHODS: A total of 290 patients with type 2 diabetes were enrolled from 5 European countries. Of these, 235 were suitable for inclusion in the analysis. Their mean age was 51.3 years and, on average, patients had had diabetes for 11 years. A discrete-choice conjoint analysis was conducted using face-to-face interviews. Treatment attributes and levels were derived from published comparative clinical trial data available at July 2001. The attributes used were: timing of injections around meals; two-hour postprandial control; effect of prandial dosing; frequency of nocturnal hypoglycaemia; and cost. RESULTS: 90% (95% CI 86-93%) of patients would choose Humalog Mix25 over Humulin 30/70, at the same cost. On average, European subjects were willing to pay €111 per month more for Humalog Mix25 (95% CI €86.71-156.91). The primary driver was the reduced risk of nocturnal hypoglycaemic events, contributing 49% of WTP. The convenience of dosing immediately prior to the meal contributed 37% and improved postprandial blood glucose concentrations contributed 14% to the WTP. Preference results were similar in all five countries, although WTP and sensitivity to increasing cost varied from country to country. The WTP values for individual countries were: France €146.83; Germany €126.65; Italy €56.98; Spain €150.06; United Kingdom €194.36. French and UK patients were relatively insensitive to increasing cost, while Italian patients were highly cost-sensitive. CONCLUSIONS: Patients in all countries showed a clear preference for Humalog Mix 25 over Humulin 30/70. WTP figures for the individual countries can be compared with the corresponding additional acquisition costs for Humalog Mix25, relative to Humulin 30/70, to assess the extent of welfare gain to the community.