TRPC1 and TRPC5 are homologues of the Drosophila transient receptor potential (TRP) protein. Both confer calcium-permeable cationic channel activity in heterologous expression systems (Beech et al 2003; Plant & Schaefer 2003). In this study we investigated expression of the proteins in human long saphenous vein, internal thoracic artery and the right atrium of the heart. Tissues were obtained from patients undergoing surgery for ischaemic heart disease (adult) or congenital heart disease (neonate) with ethical committee approval. Some saphenous vein samples had enlarged neointima. After fixation and paraffin-embedding, sequential cross-sections of tissue were processed. TRP protein expression was determined by immuno-staining using two rabbit anti-TRPC1 antibodies (Xu & Beech 2001; Alomone Labs), rabbit anti-TRPC5 antibody (Alomone Labs) and two custom-made anti-TRPC5 antibodies (made in rabbit and chicken). All custom-made antibodies had specificity confirmed by western blotting. Nerves were identified by commercial antibodies to protein S-100, synaptic vesicle 2 and protein gene product 9.5, smooth muscle by antibody to smooth muscle alpha-actin, and endothelium by antibody to CD31. In each case, staining was confirmed in at least three independent samples. TRPC1 and TRPC5 were evident in all tissues and many constituent cell types. In blood vessels, expression was prominent in smooth muscle cells but mostly undetectable in endothelium. In heart, expression was most evident in the myocardial cells and nerves but essentially absent from epicardium. There was substantial co-localisation of TRPC1 and TRPC5, as if they may function in concert. However, quantitative differences in expression were apparent. For example, TRPC5 was more strongly expressed in myocardial cells of neonatal right atrium compared with TRPC1, where as the converse was evident in the adult. Neointimal (proliferative) smooth muscle cells showed greater expression of TRPC1 relative to TRPC5 compared with medial layer (contractile) smooth muscle cells. Staining was absent in control experiments performed without primary antibody. In conclusion, TRPC1 and TRPC5 are commonly expressed and colocalised in cells of the human cardiovascular system and there is evidence for differential expression that may depend on developmental state or disease. The proteins may form a new type of calcium-permeable channel with important cardiovascular functions.