Mercury in air and in surface water has been measured during a ship expedition across the Atlantic Ocean between Hamburg (50¿N) and Buenos Aires (35¿S). The data show and interhemispherical difference of total gaseous mercury, with average concentrations of 1.56¿0.32 ng/m3 in the northern hemisphere and 1.05¿0.22 ng/m3 in the southern hemisphere. Dimethyl mercury concentrations in clean maine air are ?0.1 ng Hg/m3 or ?10% of the total gaseous mercury. The interhemispheric concentration difference and the variability of gaseous mercury of ¿16% imply a mean tropospheric residence time of atmospheric mercury of approximately 0.9 years. With a total tropospheric burden of 5.0 ¿109g, source and sink strengths are estimated to be 6¿109g mercury per year. Most of the mercury produced must originate from continental sources, by both anthropogenic and natural processes. The oceans seem to be only of minor importance in the global atmospheric mercury budget. The mercury content in water was 2--8ng/l. The mercury concentrations in air and in water did not correlate.