Two kinds of diarrhoetic shellfish toxins, okadaic acid (OA) and dinophytoxin-1 (DTX-1) were determined by micellar electrokinetic capillary chromatography (MEKC) with ultraviolet detection. A detection limit of 3.25 microg/mL for both of them was achieved. The UV absorbance of these toxins measured at 200 nm showed good linearity in the range of 6.25-200 microg/mL with R = 0.992 for OA and 0.997 for DTX-1. Three kinds of shellfish (Chlamys farreri, Mytilus edulis and Ruditaps philippinarum) collected from eight locations (sampling in the intertidal zone) along the Dalian Bay sea area of China were surveyed in February and May of 2000. Results indicated that three kinds of shellfish were contaminated by OA and DTX-1. Based on per gram of hepatopancreas in February, the contamination contents ranged from 0 to 1.26 microg for OA and from 0 to 1.82 microg for DTX-1, and in May, the contents ranged from 0 to 1.45 microg for OA and 0 to 2.56 microg for DTX-1. Among the eight locations, Hei Shi Jiao and Long Wang Tang were the most contaminated areas. Of the three kinds of shellfish, Mytilus edulis was the most significant species in accumulating OA and DTX-1.