Insecticidal activity of mixtures of pyrethroids and organophosphates or carbamates was examined using the organophosphate and carbamate-resistant (Rop-c) strain of the green rice leafhopper. When mixtures of fenvalerate plus malathion, diazinon or MPMC and phenothrin plus MTMC or BPMC were applied topically to the adult females of the Rop-c strain, the toxicity was much higher than that of organophosphates and carbamates alone, but somewhat less toxic than fenvalerate and phenothrin alone. A remarkable synergism was exhibited by mixtures of fenvalerate plus malathion in the ratios of 1.0:1.5, 1:1 and 1.5:1.0 and those of fenvalerate plus diazinon in the ratios of 1.5:1.0 and 3:1. Mixtures of fenvalerate plus MPMC also showed synergism in the ratios of 1:3 and 3:1. Toxicity of mixtures of phenothrin and MTMC or BPMC decreased in accordance with the increased ratio of carbamates to phenothrin. However, synergism was shown by mixtures combined in higher ratios of carbamates to phenothrin. Fenpropathrin and permethrin also exhibited synergism against the Rop-c strain when they were combined with malathion or MTMC at the ratio of 1:1. Dust formulations of fenvalerate plus malathion or MTMC mixtures at a ratio ranging from 1:1 to 1:5 were found to have remarkably higher insecticidal activity compared to MTMC alone. Mixtures of fenvalerate and malathion or MTMC showed synergism when applied as dust formulation at a ratio of 1:5.