RODS uses a naive Bayesian classifier called Complaint Coder (CoCo) to classify free-text chief complaints into one of the following syndromic categories: constitutional, respiratory, gastrointestinal, neurological, botulinic, rash, hemorrhagic, and other. CoCo computes the probability of each category, conditioned on each word in a free-text chief complaint and assigns a patient to the category with the highest probability. 27 The probability distributions used by CoCo are learned from a manually created training set. CoCo can be retrained with local data, and it can be trained to detect a different set of syndromes than we currently use. CoCo runs as a local process on the RODS database server. CoCo was developed at the University of Pittsburgh and is available for free download at <http://health.pitt.edu/rods/sw>.