We have shown previously that VUP was the only line out of ten human melanoma lines that failed to express the vitronectin receptor alpha v beta 3, but instead expressed alpha v beta 1. Levels of alpha v beta 1 expression were low on parental VUP cells so that iterative sorting by FACS, using an anti-alpha v antibody (13C2), was utilised to derive sublines with 8- to 10-fold higher amounts of cell surface alpha v beta 1. There was little difference between low (V-) and high (V+) alpha v beta 1-expressing sublines with regard to adherence to collagen type I, collagen type IV or laminin substrata. However, adherence to vitronectin and fibrinogen correlated closely with alpha v beta 1 expression (35-42% adhesion for V(+) lines versus 6-8% adhesion for V- lines on vitronectin, for example). Utilising a high alpha v beta 1-expressing subline (V + B2) we have shown that binding to vitronectin and fibrinogen was inhibited specifically by function-blocking antibodies to alpha v (17E6 and 14D9) and beta 1 (A11B2). V(+) sublines spread more compared with V(-) sublines on both vitronectin and fibronectin. However, neither alpha 5- nor alpha v-blocking antibodies had any effect on attachment or spreading of V + B2 on fibronectin whereas the combination of alpha 5 (PID6)- and alpha v(17E6)-blocking antibodies abrogated binding to fibronectin almost completely. This is the first report of an alpha v beta 1 integrin able to recognize vitronectin and fibrinogen, and also cooperate with alpha 5 beta 1 to mediate attachment to and spreading on fibronectin.