Using digitonin-permeabilised bovine adrenal chromaffin cells, the effects of botulinum neurotoxin light chains on exocytosis triggered by Ca 2 + or by GppNHp were examined. Botulinum neurotoxin D light chain, prepared as a His 6 -tagged recombinant protein, cleaved VAMP and substantially inhibited catecholamine release due to Ca 2 + and GppNHp. Botulinum neurotoxin C1 and E light chains produced partial inhibition of both Ca 2 + - and GppNHp-induced catecholamine release. These results suggest that Ca 2 + -dependent exocytosis and Ca 2 + - independent exocytosis triggered by a non-hydrolysable GTP analogue occurs via a SNARE-dependent mechanism in chromaffin cells.