We have established the systematic multiplex reverse transcription-polymerase chain reaction (SM RT-PCR) system of 26 members of the integrin family of genes, and used this system to investigate their expression in 25 different kinds of human adult tissues. A hierarchical clustering analysis of the tissue expression data illustrated clustering of functionally related tissues. Although the correlation was weak, bone marrow, thymus, and spleen were clustered, potentially confirming the role of certain integrin molecules in the immune response. We also investigated changes in integrin gene expression in cancer. Several differences were observed between normal and tumor, as well as between normal and cancer cell lines. The SM RT-PCR experiments for the study of alternative splicing showed that most of the integrin genes analyzed exhibited fixed ratios of differentially spliced transcripts probably due to a tissue-independent mechanism of splicing predetermined by the nucleotide sequences around the splicing donor and acceptor sites.