Ten normal subjects ingested equimolar amounts of mephenesin, mephenesin carbamate and methocarbamol, with intervals of at least one week between medications. Blood levels of drugs were followed for 4 hours, and in one case for 7 1/2 hours. In all subjects mephenesin carbamate gave higher peak values than mephenesin. Methocarbamol exceeded the other 2 drugs significantly in this regard.