The method for determination of carisoprodol concentration in the biological materials was reported. The great part of the administered carisoprodol was metabolized by liver in rats. Biological half-life of carisoprodol (150 mg./kg., i.p.) in rats was about 3 hours. The elimination of the compound with urine was about 7.5% within 48 hours. In vivo metabolism of carisoprodol was inhibited by [2,2-diphenyl-2-diethylaminoethylvaleric acid ester] SKF 525A and the duration of paralysis was prolonged. It was supposed that the principal metabolism of carisoprodol was done by a liver microsomal enzyme which requires [triphosphopyridine nucleotide reduced form] (TPNH) and oxygen.