The atmospheric concentration of peroxyacetyl nitrate (PAN) was measured over the South Atlantic Ocean in the range between 37° and 70° S inMarch 1999 in order to investigate its latitudinal distribution and its role in the NOy chemistry of the remote marine boundary layer (MBL) in the high latitudes of thesouthern hemisphere. The measurements were performed using an automatic gas chromatographic system aboard RV Polarstern. Mean mixing ratios of 62 (+/- 21)pptv were obtained between 37° and 49° S. South of 55° S, PAN concentrations were very low with values of the order of 10-30 pptv.Pronounced diurnal cycles could not be observed. The concentrations over the South Atlantic were considerably lower compared with the North Atlantic where theMBL is influenced by continental air masses.