Leishmaniasis constitutes a diverse collection of human diseases ranging in severity from a spontaneously healing skin ulcer to overwhelming visceral disease. Worldwide, two million new cases occur each year, and a 10th of the world's population is at risk of infection.1 Although the disease is highly endemic throughout northern Africa, the Middle East, parts of Europe, and Central and South America, epidemics are well recognised. For example, in southern Sudan more than 10% of the population died from visceral leishmaniasis over the past five years.

Outcome of infection is determined by interactions between the host and parasite, which are governed by the genomes of the host and parasite. It is therefore exciting to see that both host and parasite genomes have been targeted for sequence analysis.2 The leishmania genome project began as a large scale attempt to sequence part of each of the transcripts of all the genes of the organism, and the plan is now to sequence its entire genome. The genetic information from both human and parasite and the emergence of new tools such as microarray technologies will allow us to gain an understanding of the interaction between parasite virulence factors and host response factors. Molecular knowledge of the host-parasite interaction will facilitate targeting of new treatments.