Natural and anthropogenic water-soluble inorganic aerosol species are efficient cloud condensation nuclei (CCN). Biomass smoke particles, although composed mostly of organic material, are also known to be efficient CCN. However, because smoke particles consist of mixtures of organic and inorganic species, it has not been established whether the organic component is intrinsically CCN active or is intrinsically inactive and rendered CCN active only through association with water-soluble inorganic species. Here we report results of laboratory experiments on smoke particles produced by combustion of eucalyptus, redwood, and cellulose which show that their water-soluble organic fraction is principally derived from smoldering combustion of the cellulosic fuel content. Because cellulose smoke particles are entirely organic, water soluble, and CCN active (at 0.5% and 0.3% supersaturation), we conclude that the water-soluble organic species in smoke particles from smoldering biomass combustion are responsible for their intrinsic CCN activity. ¿ American Geophysical Union 1996