Hydride generation-AAS methods have been investigated for the measurement of arsenic and antimony. Continuous flow techniques for arsenic and antimony have detected limits of 0.54μg l⁻¹ and 4μg l⁻¹ respectively, which is insufficiently sensitive for unpolluted waters. Cold trap HG-AAS of arsenic(III), arsenic(V), monomethylarsenic and dimethylarsenic gave detection limits of between 0.07 and 0.1ng, and a precision of between 2.3 and 7.4% r.s.d. Semi-continuous and 'batch' hydride AAS techniques employing cryogenic trapping were developed for the determination of low levels of inorganic antimony species. Detection limits were 24ng l⁻¹ (using a 5cm³ sample) in the semi-continuous flow mode, and 17ng l⁻¹ (using a 50cm³ sample;) in the batch mode. Storage experiments indicated that samples for antimony analysis could be stored in borosilicate glass containers for up to 25 days. Water samples from the Indian and Atlantic Oceans, including the TAG hydrothermal field, have been analysed for arsenic species. Arsenic(V) was the only species present. An average concentration of 1.00 ± 0.13μg As l⁻¹ was found in Atlantic Ocean samples, and no depth effects were observed. Depth profiles at two stations in the Indian Ocean showed surface depletion of arsenic. A mean concentration of 0.98 ± 0.1μg As l⁻¹ was found in the surface waters (< 150 metres), which is significantly less than the 1.1 ± 0.15μg As l⁻¹ found at greater depth. The concentration of inorganic antimony at one station in the Indian Ocean ranged from 48ng Sb l⁻¹ to 216ng Sb l⁻¹, no systematic trends with depth were observed. The level of inorganic antimony found in North Sea surface water was 110.6 ± 13ng Sb l^-1. The spatial variation, and concentration of dissolved inorganic antimony in the river Beaulieu and rive Tamar estuaries have been investigated. In the river Beaulieu concentrations ranged from 105ng Sb l^-1 in the river end member to 208ng Sb l^-1 in the high salinity region of the estuary. In the Tamar concentrations of antimony ranged from 24ng l^-1 to 176ng l^-1. Profiles along both estuaries indicated the sea water end member to be the main contributor to the antimony load.