Aerosol optical depths (AOD) measured over Lauder in Central Otago, New Zealand in 1996–1997, and continuously since 1999, are amongst the lowest observed worldwide. The Lauder measurements show a seasonal cycle in AOD with a winter minimum and summer local maximum, and there is a springtime peak that is probably due to biomass burning. The wavelength dependence of AOD suggests a relatively stable size distribution but smaller average particle size in spring. Lack of correlation with surface humidity below 90% RH, in both AOD and wavelength dependence, may constrain the likely composition of the aerosol. There was a downward but insignificant trend in mean AOD over the measurement period.