Abstract. We consider a simple divergence-free language RP for reactive processes which includes prefixing, deterministic choice, action-guarded probabilistic choice, synchronous parallel and recursion. We show that the probabilistic bisimulation of Larsen and Skou is a congruence for this language. Following the methodology introduced by de Bakker and Zucker we give denotational semantics to this language by means of a complete metric space of (deterministic) probabilistic trees defined in terms of the powerdomain of closed sets. This new metric, although not an ultra-metric, nevertheless specialises to the metric of de Bakker and Zucker. Our semantic domain admits a full abstraction result with respect to probabilistic bisimulation.