An automated system for protein crystallization trials is described. Similar to commercial systems in operation, this system is readily assembled at a far lower cost. The software runs on either a microcomputer or a VAX and is both versatile and readily modified for special requirements. The system is capable of pipetting polyethylene glycol solutions accurately. Root-mean-square deviations in the accuracy of pipetted well solutions were similar to results obtained manually. Factors influencing reproducibility are discussed.