The Ca2+ antagonists are a chemically heterogeneous group of drugs which share the common property of attenuating Ca2+ influx through voltage-activated L-type Ca2(+)-selective channels. At least six criteria have been used as a basis of their classification: specificity of Ca2+ current inhibition, chemistry, tissue selectivity, salicylate sensitivity, calcium modulation and receptor specificity. Tissue selectivity provides a useful approach to classification and provides a useful basis on which to equate their relative usefulness as therapeutic agents. The basis of the tissue selectivity is probably complex and dependent not only upon the chemistry of the antagonist but also upon tissue-dependent differences in the composition of the alpha 1 subunit of the binding complex.