A comparative study was conducted in 1995-96, during 8 months, on biodegradation of several types of cigarette butts, in natural (B1) and laboratory (B2) environments. Non filter cigarette butts were compared with filter butts made of cellulose acetate, or paper, or dual (acetate + paper). The « trapping ≈ technique was used to follow in time : weight loss, microbial numbers (bacteria + fungi) and material degradation with the help of electron microscopy (transmission and scanning). In both biotopes, non filter butts were degraded faster than paper filter butts. Cellulose acetate filters decomposed most slowly. No important microbiological differences appeared between bacterial or fungal populations degrading the various types of butts. In natural conditions, microfauna (Acari, Miriapods...) played an important role in physical destruction of butts. Smoke residues in butts apparently had a slowing effect on biodegradation in the first two months of the experiment. Ultrastructurally, TEM and SEM observations revealed that cigarette butts, whatever their type, behaved as any organic debris regarding biodegradation. Cellulose acetate fibers constitute the element most slowly biodegradable in natural conditions. The establishment of links between microorganisms and clay particles, to constitute aggregates, could partly explain the slowing down of butt weight loss from the second month onwards in the experiment.