The basis of a cloud condensation nucleus (CCN) climatology program has been in place at Cape Grim (Tasmania) since 1982. This has shown both marked seasonal variation and evidence of interannual variation in CCN concentration. CCN concentrations have been found to be substantially understandable in terms of the condensation or Aitken nucleus (CN) concentration and size. Whether CCN concentrations are systematically changing in response to climate change and/or increasing anthropogenic sulfur emission is an unresolved question. Although present CCN concentrations are higher than those reported for clean oceanic regions two decades earlier the data do not allow confident conclusions about the cause. ¿ American Geophysical Union 1990