One solution to the estimation of product reliability during the development phase is to measure reliability improvement over time and compare this improvement (growth) to previous product development progress. This paper uses the Duane's reliability growth model and applies it to some subsystems of light duty trucks during their design and development and prototype testing. The data presented illustrates explicitly the prediction of the reliability growth during development and testing. The data is used to estimate the parameters for the reliability growth curve. Once the model is developed, it can be used to monitor product reliability.