The inhibitory effects of a naturally occurring diterpenoid furanolactone, columbin, on partially purified acidic phospholipase A 2 (PLA 2) from Naja nigricolis was investigated. Columbin inhibited the N. nigricolis PLA 2 in a dose related pattern with an IC 50 value of 2.5 μM. Double reciprocal plots of initial velocity data of inhibition by columbin revealed a non-competitive pattern. The K M remained constant at 19 μM, while the V max changed from 54 μmoles/min/mg to 32 μmoles/min/mg and 20 μmoles/min/mg in the presence of 2 and 10 μM of columbin, respectively. Extrapolated K i values were 3 and 6.28 μM at 2 and 10 μM inhibitor, respectively. Columbin also inhibited PLA 2 hydrolysis of ghost RBC in a dose-dependent fashion. At least 70% suppression of PLA 2 -catalysed haemolysis of RBC was observed in the presence of 2 μM columbin.