This paper examines actual and contingent participation by Dutch arable farmers in biodiversity conservation programmes. Probit and Tobit modelling were used to analyse the effect of farm and farmer characteristics and farmer attitudes on participation. The optimal bid offer was derived from a referendum contingent valuation (CV) survey for a proposed field margin programme. The results indicate that actual and contingent participation are better explained by the production environment and by familiarity with conservation programmes than by farmer characteristics or field characteristics. Contingent participation was significantly affected by farmers' perceptions of weed risks. The CV experiment suggested that up to 60 per cent participation might be achieved with appropriate bid offers.