The effects of cold pretreatment, AgNO3 and activated charcoal on haploid plant production from unpollinated sugar beet ovules were investigated. Both cold pretreatment and the addition of charcoal increased the frequency of embryo formation, whereas AgNO3 decreased or completely inhibited it. Colchicine (50, 100, 150 or 500 mg l(-1)) and trifluralin (1.7, 3.4 or 5.0 mg l(-1)) for 12, 24, 36 or 48 h were compared in agar-solidified, agarose-solidified or liquid media. Although colchicine gave a higher doubling rate (25.3%) than trifluralin (18.2%), the difference was not significant. Both agents were more effective when used in liquid (29.1%) than agarose-solidified medium (20.7%) and agar-solidified medium (15.4%). A treatment duration of 48 h was significantly more effective (27.5%) than 12 h (13.6%) but it was not different from 24 h (16.3%) or 36 h (18.6%).