Abstract
Immature gametocytes (stages I—III) of Plasmodium falciparum are readily killed by chloroquine at a concentration of 0·1 nmol ml−1. The morphological effects of this drug at the ultrastructural level appear very similar to those described previously for the asexual parasites. Lesions were classified into four groups, disorganization of food vacuole; pellicular modifications; mitochondrial changes, and nuclear modifications. The timing and sequence of development of these lesions strongly suggest that the drug acts quickly through disruption of food vacuole activity with consequent secondary metabolic effects. Direct effects on the parasites' chromatin are considered unlikely for nuclear division was frequently recorded in grossly distorted cells.