A spectrophotometric method for the determination of amoxycilline trihydrate and flucloxacilline monohydrate alone or in mixture and pharmaceutical preparation is described using 3,5-dinitrobenzoic acid. The procedure does not require any separation step. The calibration curves are linear upto 1 – 24 µg/ml for amoxycilline at room temperature and 1 - 30 µg/ml of flucoxacilline at 60 ± 2 ºC after heating time 30 min. the proposed method was applied to determine the studied drugs in synthetic mixture and in pharmaceutical preparations (vails, cupsules, and syrup) containg each or both of them. Quim. Anal., 89, 726–729 (1993).