Once platelets are activated, the first event tooccur is a rapid change in shape, associated with Ca 2+ /calmodulin-dependent myosin light chain (MLC) phosphorylation and withRhokinase activation. The purpose of this studywas to investigate which is the biochemical pathway that leads to platelet shape change in response to convulxin, a selective GpVI activator, and to verify whether MLC phosphoryla-tion is essential for this process.