MEKC coupling with LIF detection has been used for the determination of four aflatoxins (B-1, B-2, G(1) and G(2)). Separations were performed in an uncoated fused-silica capillary (70 cm x 75 mu m id, 55 cm effective length), using 20 mM borate buffer with 30 mM SDS (pH 8.5) and 7% ACN. In order to increase sensitivity, an on-line preconcentration procedure was applied, based on sweeping, using the same separation buffer without SDS as solvent of the sample. The precision of the method was evaluated in terms of repeatability and intermediate precision and the results were acceptable in all cases (RSD < 12%). With the on-line preconcentration LODs (obtained as 3 x S/N) were as low as 0.11, 0.52, 0.04 and 0.10 mu g/L for G(2), G(1), B-2 and B-1, respectively. Recovery studies were developed with extracts of rice samples spiked with aflatoxins, being in the range between 93.0 and 105.4%. The method has also been applied to the determination of aflatoxins in rice samples, and the results compared with those obtained by a standard method, being in good agreement.