Dispersed rat islet cells embedded in a matrix of collagen I are known to form aggregates in vitro reminiscent of native islets. Furthermore, it appears that islet function and survival are better maintained in vitro when cells are grown in the presence of extracellular matrix. These studies suggest an important role of cell--matrix interactions in the formation and maintenance of islet structure and function. The molecular basis of these interactions is mostly unknown. In the present study, we confirm the presence of beta 1 integrins on primary and transformed (RIN-2A line) rat islet cells. Perturbation studies in vitro show that beta 1 integrins play a role in islet cell attachment and spreading on bovine extracellular matrix and on the matrix produced by A-431 cells. The alpha 3 integrin subunit is coimmunoprecipitated with beta 1 from extracts of both primary and transformed islet cells, and immunodepletion studies suggest that alpha 3 beta 1 represents nearly half of the total beta 1 integrins expressed on primary islet cells. In situ, alpha 3 and beta 1 are expressed on the surface of all islet cell types, as shown by indirect immunocytochemistry on paraformaldehyde-fixed sections of rat pancreas. In conclusion, the study demonstrates the presence of alpha 3 beta 1 on primary and transformed rat islet cells, and an important role of beta 1 integrins in islet cell attachment and spreading in vitro.