Isolation and cloning of abundant reverse transcriptase-polymerase chain reaction (RT-PCR) products from the filarial nematode Brugia malayi using the conserved nematode spliced leader sequence and poly A as amplification targets has allowed us to identify abundant, stage specific transcripts from infective and post-infective larvae. The predicted protein products of the most prominent full-length transcripts from mosquito-derived L3 parasites are: (i) Bm-ALT-1, a homologue of a Dirofilaria immitis abundant larval protein: (ii) Bm-CPI-1, a cystatin-type cysteine protease inhibitor; (iii) Bm-ALT-3, a novel predicted 6 kDa glycine/tyrosine-rich protein; and (iv) Bm-TPH-1, a homologue of a mammalian translationally-controlled tumour protein. Some transcripts were not full-length but had mis-primed at A-rich stretches of coding sequence: the most abundant of these was Bm-col-3, a which encodes a collagen homologous to Bp-COL-1 of Brugia pahangi. Similar analysis of abundant spliced leader (SL)/oligo-dT products from fourth-stage larvae 9 days post-infection yielded two dominant transcripts: (i) Bm-cdd-1, which encodes a protein with homology to cytidine deaminase, differing at only one amino acid position from its homologue described in Brugia pahangi; and (ii) the same truncated form of Bm-col-3 found in L3 preparations. Expression of the major transcripts was assessed by PCR amplification of cDNA libraries derived from each stage of the life cycle. alt1, alt-3 and cpi-1 were all found to be specific to the L3 stage, while cdd-1 was found only in the L4 cDNA library. Expression of these larval-specific transcripts was not detected in either microfilarial or adult libraries.