Benoxaprofen plasma profiles were obtained in two groups of elderly female patients. A single dose of benoxaprofen, either 600 mg or 300 mg, was given and blood levels were measured daily to 120 hours. Mean peak plasma levels were reached at five hours following the 600-mg dose and at seven hours after the 300-mg dose. Elimination half-lives calculated from levels during 36-120 hours resulted in means of 111 hours and 86.4 hours for the 600-mg and 300-mg doses respectively. (Normal subjects, 30 to 35 hours.) Because of these extended half-lives, a further study was conducted following a single 600-mg dose to four more patients. Blood vessels were measured up to 504 hours (21 days). This resulted in a means half-life of 147.9 hours calculated from levels during 168-504 hours. Although serum creatinine levels ere not generally above the normal for this age group, calculated creatinine clearances were considerably reduced. It is concluded that the high plasma benoxaprofen levels achieved, combined with the slow clearance rates and long half-lives, indicate that it may be possible to work is needed to determine whether this prolonged half-life is matched by an equally prolonged therapeutic effect.