The paper presents new Grid application workflow paradigm based on advanced control mechanisms provided by synchronizers. Synchronizers generate program execution control decisions based on predicates computed on global application states. We propose that execution control by synchronizers is used to co-ordinate parallel applications executed on Grid. For this, we extend the graphical parallel program design environment PS-GRADE by Grid level synchronizers. Grid and application level synchronizers co-operate by sending state reports and receiving control signals over Grid communication network. Open Grid Services Infrastructure, implemented using Globus toolkit, is used for these purposes.