A new, automatic method for the clean-up, preconcentration, separation, and quantitation of nonsteroidal anti-inflammatory drugs (NSAIDs) in biological samples (human urine and serum) using solid-phase extraction coupled on-line to capillary electrophoresis is proposed. Automatic pretreatment is carried out by using a continuous flow system operating simultaneously with the capillary electrophoresis equipment, to which it is linked via a laboratory-made mechanical arm. This integrated system is controlled by an electronic interface governed via a program developed in GWBasic. Capillary electrophoresis is conducted by using a separation buffer consisting of 20 mM NaHPO4, 20 mM beta -cyclodextrin and 50 mM SDS at pH 9.0, an applied potential of 20 kV and a temperature of 20 degreesC. The analysis time is 10 min and the detection limits were between 0.88 and 1.71 mug mL(-1). Automatic clean-up and preconcentration is accomplished by using a C-18 minicolumn and 75% methanol as eluent. The limit of detection of NSAIDs can be up to 400-fold improved when using sample clean-up. The extraction efficiency for these compounds is between 71.1 and 109.7 mug mL(-1) (RSD 2.0-7.7%) for urine samples and from 77.2 to 107.1 mug mL(-1) (RSD 3.5-7.1%) for serum samples.