Energy saving, in battery operated wireless sensor networks, for the purpose of increasing the node and network lifetime, has gained substantial importance. This research was conducted with the objective of reducing the power consumption of the MICA2 sensors. The objective was pursued by manipulating the MAC layer, and by introducing a dynamic transmission power control algorithm. A new simulation tool was developed in order to reduce the complexity related to the design and testing of the transmission power control algorithm. The power control algorithm was also developed in the NesC language for the MICA2 sensors. In addition,several modifications were introduced to the original MAC protocol. Data, derived from both simulations and experiments, demonstrated that a significant reduction in energy expenditure was achieved, for the MICA2 sensors. In addition,the data revealed that the network lifetime was extended. This research dramatically illustrated the energy saving potential of the application of transmission power control procedures in wireless sensor networks.