Starting with a cloned cDNA encoding human ribosomal protein S24 [Brown et al., Gene 91 (1990) 293-296], we PCR-amplified two introns from the human RPS24 locus. These then were used as unique nucleic-acid probes to isolate a 12-kb RPS24 gene fragment from a library of human genomic DNA. The nucleotide sequence of human RPS24 (4942 bp), its exon-intron organization and mRNA transcription start point were determined using standard procedures. RT-PCR analyses of S24 mRNAs from multiple human tissues and cell lines revealed two mRNA isoforms which differ from each other, as well as murine S24 mRNAs due to alternative exon splices near the 3' end of the gene.