In order to estimate arsenic flux from the English Channel toward the North Sea, 168 samples were obtained from September 1990 to November 1991 along a transect between Boulogne and Folkestone comprising six stations and two depths. Organic and inorganic arsenic were measured in dissolved phase and total arsenic in suspended particles. The mean concentration of dissolved total arsenic in water was 1.38 +/- 0.12 mug.l-1. The variability of measured concentrations was low, particularly for the four intermediate stations. Results were slightly more sensitive for English (1.38 +/- 0.12 mug.l-1) and French (135 +/- 0.11 mug.l-1) coastal stations due to exchanges with shallower sediments. Dissolved organic arsenic was nearly negligible from December to March (< 1%) and maximal from July to September, essentially in the form of dimethylarsinic acid. It constituted about 10% of dissolved total arsenic and was related to phytoplankton activity. The lowest concentrations of dissolved total arsenic (1.26 +/- 0.03 mug.l-1) were also measured in July. Arsenic in suspended particles (0.16 +/- 0.19 mug.l-1), which accounted for only a small portion (i.e. 8.5%) of the total arsenic in the water column, was more elevated (20%) near the English coasts (0.30 +/- 0.25 mug.l-1). Mean concentrations for particles were 22.2 mug.g-1, and the distribution coefficient with water was log(K(d)) = 4.14 +/- 0.24. The flux from the English Channel toward the North Sea from 1 October 1990, to 1 October 1991, was 4,442 tons of dissolved arsenic and 412 tons of particulate arsenic.