PKC beta I and PKC beta II are DAG- and Ca(2+)-dependent conventional or classical isoforms of protein kinase C. Generated by alternative splicing from a single gene, they differ at their C-terminal 50 (beta I) or 52 (beta II) residues. They are expressed as major PKC isoforms in a variety of tissues, and thus the functions ascribed to "PKC" based on early studies using phorbol esters and PKC inhibitors could be attributed to them. As tools to probe into isoform-specific functions have recently become available, our understanding of the normal functions of these isoforms has dramatically increased. This minireview will focus mainly on two areas of signal transduction where the roles of PKC beta I and PKC beta II are relatively well-characterized: immunoreceptor and insulin receptor systems. Their involvement in disorders due to pertubations in these signaling systems, i.e., immunodeficiencies and diabetes, is also reviewed. Finally, patterns of PKC action in these and other biologic systems are discussed.