EWOC 2.0: interactive software for dose escalation in cancer phase I clinical trials. Escalation With Overdose Control (EWOC) version 2.0 is a publicly available freeware that uses Bayesian methods in a dose escalation scheme to assign dose levels sequentially to patients in cancer phase I clinical trials. The methodology is based on the optimal Bayesian-feasible procedure, which is designed to approach the maximum tolerated dose as fast as possible while controlling the probability of overdosing patients. This article describes the methodology as well as the development of the application program. Features of EWOC 2.0 are demonstrated.