The fission yeast Schizosaccharomyces pombe has recently been established as an experimental model for the study of antisense RNA-mediated gene suppression. To validate the use of S. pombe as a host for identifying antisense genes for use in human cells, it was important to determine if sequences identified in yeast were as equally effective in a human cell line. This report describes the comparison of a range of lacZ antisense RNAs targeting a lacZ gene expressed in HeLa cells in a comparable manner to its expression in S. pombe cells in earlier studies; In both cell types, the same lacZ gene target was expressed using the same promoter. Antisense genes were expressed episomally in both experimental systems and the levels of suppression determined. In all cases, the relative level of suppression of the lacZ gene was similar in the mammalian and yeast cells. This result indicates that, at least for lacZ antisense RNA, results obtained in fission yeast are predictive of their behavior in the mammalian cellular environment,