We present an operon predictor for prokaryotic operons (PPO), which can predict operons in the entire prokaryotic genome. The prediction algorithm used in PPO allows the user to select binary particle swarm optimization (BPSO), a genetic algorithm (GA) or some other methods introduced in the literature to predict operons. The operon predictor on our web server and the provided database are easy to access and use. The main features offered are: (i) selection of the prediction algorithm, (ii) adjustable parameter settings of the prediction algorithm, (iii) graphic visualization of results, (iv) integrated database queries, (v) listing of experimentally verified operons, and (vi) related tools.