This study was carried out to investigate toxicity of insecticide carbofuran and compensatory effects of phenobarbital sodium (PB) in vivo and in vitro. Sprague Dawley male rats were used as experimental animals and divided into carbofuran only administered group and simultaneous application group of carbofuran and PB. At 30 rain and 1, 3, 6, 12, 24, 48 and 96 hrs after each treatment, the animals were sacrificed by decapitation. Kidney were immediately removed, immersed in fixatives, and processed with routine method for light microscopic study. Paraffin sections were stained with H-E, PAM and PAS. $5.0 imes 10^4$ cell/ml of NIH 3T3 fibroblast in each well of 24 multidish were cultured: After 24 hours, the cells were treated with solution of six groups; control group cultured in media only, carbofuran $MTT_50$ or $NR_50$ group cultured in the media containing carbofuran $MTT_50$ or $NR_50$ and four experimental groups cultured in the media containing carbofuran $NR_50$ plus various concentratins of PB. After the NIH 3T3 fibroblast of all groups were cultured in same condition for 48 hours, Tetrazolium MTT (MTT) and NR (neutral red) assay were performed to evaluate the cytotoxicity of cell organelles. Under the light microscope, atrophic change of renal corpuscles were frequently observed in 1 and 2 days after carbofuran treatment. The increase of the mesangium was apparent in 1 and 2 days after carbofuran treatment. Necrotic changes of the epithelium and loss of brush border of proximal tubules were most severe at 2 and 3 days after carbofuran treatment, respectively. In contrast, there were no evidences of the toxic effects on renal tissues at 48hrs in carbofuran-PB treated groups. Carbofuran $MTT_50$ and $NR_50$ were 78$mu M$, 82.5$mu M$ respectively. MTT and NR quantities were significantly increased in carbofuran-PB 100$mu M$ treatment group and carbofuran-PB 100$mu M$ treatment group. On the basis of these results, it is obvious that PB has compensatory effects against carbofuran toxicity.