A stochastic pi calculus for concurrent objects. We present SpiCO, a new modeling and simulation language for systems biology. SpiCO is based on the stochastic $pi $ calculus. It supports higher level modeling via multi-profile concurrent objects with static inheritance. We present a semantics for SpiCO in terms of continuous time Markov chains, and show how to compile SpiCO back into the biochemical stochastic $pi $ calculus while preserving semantics.