Summary Kala azar or visceral leishmaniasis, a parasitic disease caused by Leishmania donovani, is presently causing an epidemic in the eastern region of India. Diagnosis of kala azar is often complicated. We developed a pair of oligonucleotides suitable as primers from the variable region of a predominant sequence class of minicircles of L. donovani. These primers were used in a nonisotopic polymerase chain reaction and found to be highly specific for the parasites of L. donovani complex. Using these primers, amplification of L. donovani kinetoplast DNA minicircle from the peripheral blood of kala azar patients results in a product of 204 bp. The patient group was comprised of individuals from a highly endemic region of India. We feel that PCR could assess the efficacy of new leishmanicidal drugs under investigation in these patients. PCR could also predict response to therapy which would be useful for both clinical and research applications.