Platelet deposition on collagen under flow requires signal transduction through the adaptor SLP-76. Whole blood from the indicated mice was perfused over collagen-coated glass slides at wall shear rates at and between 400 and 1300 s^–1 for 4 minutes. (A) Percent surface coverage of SLP-76–deficient (▪;n = 5) and the wild-type (□;n = 3) platelets after whole blood perfusion over a collagen-coated surface. The results shown are the mean ± SEM. Statistical significance was seen between the SLP-76–deficient platelets and the control (P < .01) at the specified shear rates. (B) Representative phase-contrast images after perfusion. The lines seen in the upper left portions of some panels are visual artifact and do not arise due to abnormalities in the collagen-coated surface.