A WSN is envisaged to consist of a large number of nodes, each combining sensing, processing and wireless communication capabilities. The nodes have to cooperate to achieve a global function required by the user. Towards achieving this goal, multiple tasks are performed on all nodes or a subset of nodes in the network. The subject of this paper is the synchronized execution of periodic tasks at different nodes, for example: sensing tasks or a periodic on/off switching of radio transceivers. The method is based on synchronizing timer interrupt occurrences at different nodes to a single reference, leading to tight synchronization of tasks over nodes. Measurements show that task synchronization is achieved on our hardware platform with an average time difference of 5 μs between the starts of temporally related tasks on different nodes.