Transformation of the free-living nematode Caenorhabditis elegans with promoter/reporter gene constructs is a very powerful technique to examine and dissect gene regulatory mechanisms. No such transformation system is available for parasitic nematode species. We have exploited C. elegans as a heterologous transformation system to examine activity and specificity of parasitic nematode gene promoters. Using three different parasite promoter/lac Z reporter constructs strict tissue-specific expression is observed. Upstream sequences of the Haemonchus contortus gut pepsinogen gene pep-1 and cysteine protease gene AC-2 direct expression exclusively in gut cells, while promoter sequence of the Ostertagia circumcincta cuticular collagen gene colost-1 directs hypodermal-specific expression. Mutation analysis indicates that AC-2 promoter function is dependent on a GATA-like motif close to the translation start site, similar to our findings with the C. elegans cpr-1 cysteine protease gene. While the spatial expression of these parasite promoters in C. elegans correlates with their expression in the parasite, the exact timing of expression does not. This suggests that regulatory mechanisms influencing the timing of expression may have evolved more rapidly than those controlling spatial expression of structural genes.