This Phase I SBIR proposal concerns PC software to compute sample size and statistical power for the design of biomedical studies. For Phase I, our program will implement two novel simulations for the design of time-to- event studies: a method of Halpern and Brown [1987] that uses existing survival data, perhaps taken from published articles, to estimate sample size and power for a new study, and a method we developed for studies in which accumulating survival data are re-analyzed at each update. Phase I will also include a power calculation for repeated measures (longitudinal) studies with continuous outcomes. None of these is available in current design software. Our Phase II package will include easy, graphical exploration of tradeoffs between design features, calculations for a wide range of clinical and epidemiological designs and context-sensitive advice to the intended user (e.g., physician concerned with study design or statistician). Recent reviews of this product category suggest a substantial demand for comprehensive, flexible design software for medical, environmental and industrial studies but that the current state is unsatisfactory. We have studied these reviews and the software and believe that our proposed product is more informative, more comprehensive, and more attractive.