Colchicine, a drug which poisons the polymerization of microtubules, was assayed for effects on the invasion of Plasmodium falciparum merozoites into red cells in order to investigate if merozoite microtubules have a function in invasion. Culture conditions and concentrations of colchicine were established where the maturation and rupture of schizonts was unaffected by the drug. This was judged first by light microscopy, including morphology and counts of nuclear particle numbers, then by ultrastructural studies which excluded deranged organellogenesis as a cause of merozoite failure, and finally by diachronic cultures in which both recruitment and loss of schizonts could be counted. Specific invasion inhibition was seen when 10 μM–1 mM colchicine was present. Red cells pre-incubated in colchicine and then washed showed no reduction in their extent of invasion, and neither red cell lysis, sphering nor blebbing were apparent. We conclude that intact microtubules are necessary for successful merozoite function.