We examined chronological changes in muscle relaxation in ICR mice after p. o. administration of ethanol. The effect of ethanol was found to be dose-dependent. We also carried out an investigation to determine whether or not the muscle relaxation induced in mice by ethanol and acetaldehyde-induced acute toxicity could be suppressed by sesamin. When sesamin (500mg/kg/day) was administered p. o. for 7 or 14 consecutive days, the muscle relaxation induced by ethanol (1.5g/kg, p. o.) was markedly suppressed. Sesamin pretreatment also markedly prevented acetaldehyde-induced acute toxicity (LD₅₀) in mice, but the ethanol clearance in blood did not show any significant changes. We have not yet determined the mechanism by which sesamin inhibits ethanol-induced muscle relaxation, although the effects seen unlikely to be due to enhanced clearance of ethanol alone.