It is generally well accepted that caveolin-3 expression is muscle-specific, whereas caveolin-1 and -2 are co-expressed in a variety of cell types, including adipocytes, endothelial cells, epithelial cells, and fibroblasts. Caveolin-1 and -2 are known to form functional hetero-oligomeric complexes in cells where they are coexpressed, while caveolin-3 forms homo-oligomeric high molecular mass complexes. Although caveolin-2 might be expected to interact in a similar manner with caveolin-3, most studies indicate that this is not the case. However, this view has recently been challenged as it has been demonstrated that caveolin-2 and -3 are co-expressed in primary cultures of cardiac myocytes, where these two proteins can be coimmunoprecipitated. Thus, it remains controversial whether caveolin-2 interacts with caveolin-3. Here, we directly address the issue of caveolin isoform protein-protein interactions by means of three distinct molecular genetic approaches. First, using caveolin (Cav)-1 deficient mouse embryonic fibroblasts in which we have stably expressed caveolin-1, -2, or -3, we find that caveolin-1 interacts with caveolin-2 in this setting, while caveolin-3 does not, in agreement with most published observations. Next, we used a transfected L6 myoblast cell system expressing all three caveolin proteins. Surprisingly, we find that caveolin-1, -2, and -3 all co-immunoprecipitate in this cell type, suggesting that this interaction is muscle cell-specific. Similar results were obtained when the skeletal muscle of caveolin-1 transgenic animals was analyzed for caveolin-1 and caveolin-3 co-immunoprecipitation. Thus, we conclude that all three caveolins can interact to form a discrete hetero-oligomeric complex, but that such complex formation is clearly muscle-specific.