Fipronil seed treatments were evaluated to determine whether they directly in¯uence germination and subsequent seedling growth in rice (Oryza sativa L). Continuous seed exposure to ®pronil (four days) at 2 000 mg litre À1 signi®cantly impaired germination (P 0.001). When exposure was restricted to a 1-h period 48 h after the initiation of germination, early post-germination growth was also impaired (assessment two days after exposure, P 0.05). The proportion of seeds satisfying our criteria for normal germination fell by 2.3 and 2.6% respectively across 17 cultivars. Cultivar effects were highly signi®cant (P 0.001). When exposure to ®pronil (2 000 mg litre À1 ) was restricted to 2 h at initial seed wetting no signi®cant growth impairment occurred. No signi®cant differences (P b 0.05) were found between shoot lengths or root system dry weights of control plants and plants developing from seed exposed continuously (two days) to ®pronil at rates of up to 2 000 mg litre À1 during germination and harvested nine days after sowing. Treating germinated seed with ®pronil for 1 h immediately prior to sowing at rates of up to 4 000 mg litre À1 did not result in signi®cant changes (P 0.05) in plant growth parameters at either nine or 25 days after sowing. No evidence of ®pronil having a direct phytostimulatory effect on rice was obtained.