Leishmania donovani, a protozoan parasite, causes visceral disease in humans. In order to identify genes that control growth, we have isolated for the first time in the order Kinetoplastida a gene encoding for centrin from L. donovani. Centrin is a calcium binding cytoskeletal protein essential for centrosome duplication or segregation. Protein sequence similarity and immunoreactivity confirmed that Leishmania centrin is a homolog of human centrin 2. Immunofluorescence analysis localized the protein in the basal body. Calcium binding analysis revealed that its C-terminal Ca2+ binding domain binds 16 fold more calcium than the N-terminal domain. Electrophoretic mobility shift of centrin treated with EGTA and abrogation of the shift in its mutants lacking a Ca2+ binding site suggest that Ca2+ binding to these regions may have a role in the protein conformation. The levels of centrin mRNA and protein were high during the exponential growth of the parasite in culture and declined to a low level in the stationary phase. Expression of N-terminal deleted centrin in the parasite significantly reduces its growth rate and it was found that significantly more cells are arrested in the G2/M stage than in control cells. These studies indicate that centrin may have a functional role in Leishmania growth.