Chemical investigation of an alkaloidal extract of Alstonia macrophylla bark led to the isolation and identification of two new nitrogenous derivatives, alstoniaphyllines A (1) and B (2), a new indole alkaloid, alstoniaphylline C (4), and eight known alkaloids (3, 5-11). Alstonisine (9) exhibited antiplasmodial activity against Plasmodium falciparum, with an IC50 of 7.6 μM.