Latex from Calotropis procera is widely used in folk medicine as a rich source of biologically active compounds capable of promoting diverse benefits such as control of dermal fungal infections, antimicrobial activities and pain relief among other useful properties. The aim of this work was to characterize the anti-inflammatory effect of a non-dialysable protein fraction recovered from the rubber-free latex using three different experimental models when administrated intravenously. In vivo neutrophil migration induced by carrageenin (500 microg) was severely inhibited by doses of latex proteins reaching maximum inhibition (80%) at 100 mg/kg. Paw edema exacerbated by the effect of carrageenin was almost completely suppressed after 4 hours and was controlled within the first hour following latex protein administration. However, the same latex fraction was completely unable to control the paw edema invoked with dextran stimulation (400 microg), suggesting that the inhibitory effect of the latex is likely to be cell-mediated. Iphosphamide-induced vesical edema in mice was also largely prevented by the latex protein fraction. These results indicate that an effect similar to that of mesna, the classical drug used for this purpose, is operative. Our findings suggest that the sample tested seems to act over a wide spectrum as a novel anti-inflammatory agent. The results also suggest that the active molecules are of a proteinaceous nature despite the presence of numerous secondary metabolites naturally occurring in the C. procera latex.