We describe the isolation and characterisation of two novel genes of the parasitic protozoan Leishmania major that are related by nucleotide sequence homology to eukaryotic genes encoding 70 Kd. heat shock proteins. The transcription of neither gene is heat-inducible but both are constituitively-expressed throughout the promastigote stage of the parasite life cycle. A third gene shows differential expression between non-infective and infective promastigote stages in the absence of any temperature change. These genes are related by sequence homology to the tandemly-repeated hsp70 genes of trypanosomatids, but are located on different, dispersed chromosomes within the genome of L. major. The open reading frame for translation derived from one of these sequences contains a putative mitochondrial signal peptide at its amino-terminus.