Despite elevated cathepsin L mRNA levels in kidney tumors, cathepsin L protein/activity was scarcely detectable in these tumors. As a possible reason, we detected two new splice variants of human cathepsin L mRNAs not identical to those previously reported. Besides the normal 'full-length' mRNA (hCATL-A) there is one form lacking 27 nucleotides (hCATL-A I) and another form lacking 90 nucleotides (hCATL-A II) in exon I. The splice variants do not influence the amino acid sequence of the translational product. hCATL-A and hCATL-A I probably form a secondary structure at the 5' non-coding sequence not present in hCATL-A II.