A number of antibiotics have been reported to disturb the decoding process in prokaryotic translation and to inhibit the function of various natural ribozymes. We investigated the e ect of several antibiotics on in vitro splicing of a eukaryotic nuclear pre-mRNA (b-globin). Of the eight antibiotics studied, erythromycin, Cl-tetracycline and streptomycinwere identi®ed as splicing inhibitors in nuclear HeLa cell extract. TheKi values were 160, 180 and 230lM, respectively.