Integrins are a large and complex family of membrane spanning alpha beta heterodimeric cell surface glycoproteins mediating cell/cell and cell/matrix interactions. Small, round, blue cell sarcomas (SRBCS) are a group of poorly differentiated tumours of various and in part uncertain histogenesis displaying similar cytomorphology. Among them are rhabdomyosarcomas (RMS), ganglioneuroblastomas [(G)NB], primitive peripheral neuroectodermal tumours (pPNET) and Ewing's sarcomas (ES). Thirty-two SRBCS were studied immunohistochemically for the distribution of beta 1, beta 3 and beta 4 integrins in situ. We found complex and to some extent differential patterns of beta 1, beta 3 and beta 4 integrin subunit expression in different types of SRBCS: all of the sarcomas studied were consistently beta 1+, beta 4-, alpha 2-. Four of nine RMS were completely negative for all other integrin subunits studied while one RMS was alpha 5+ throughout and three RMS were focally alpha 5+. Three RMS expressed the alpha 6 and alpha v chains. In contrast to RMS, pPNET and ES, all of which were alpha 1-, alpha 3-, (G)NB were alpha 3+ and frequently co-expressed alpha 1. The eight pPNET and seven ES studied showed a similarly restricted integrin profile that was limited to the expression of beta 1 and alpha 5 in nearly all cases. In summary, RMS were beta 1+, alpha 1-, alpha 3- and heterogeneously expressed alpha 5 and alpha 6. (G)NB were generally beta 1+, alpha 1+, alpha 3+, alpha 5-, alpha 6-. pPNET and ES were beta 1+, alpha 1-, alpha 3-, alpha 5+, alpha 6-. The data illustrate a complex expression pattern of various integrins in SRBCS, a differential expression pattern of some of the integrin subunits among different types of SRBCS and almost identical integrin profiles in pPNET and ES.