BRE, a putative stress-modulating gene, found able to down-regulate TNF-alpha -induced NF-kappaB activation upon overexpression, is now shown in human cells expressed as multiple m-RNA isoforms. A total of six isoforms are produced by alternative splicing predominantly at either end of the gene. Predicted from the cDNA sequences of these isoforms, three of them (alphaa, alphab, and alphac) code for BRE of different C-terminus, and the other three (betaa, betab, and betac) may possibly be the nonfunctional counterparts. All human cells examined coexpress all the predominant splice variants, albeit at different ratios. Comparing with normal cells, immortalized human cell lines uniformly express higher levels of BRE. Interestingly, peripheral blood monocytes responded to LPS by down-regulating the expression of all the BRE isoforms, which was however less obvious in the cell fine counterpart, THP-1. Isoform aa, which codes for the canonical BRE with a C-terminal peroxisomal targeting sequence, is the most abundant transcript. We propose that the function of BRE and its isoforms is to regulate peroxisomal activities.