Recent technological developments have revolutionized the design and operation of warehousing systems. Automated storage and retrieval systems (AS/RS) driven by embedded computers are becoming increasingly more prevalent. The increased use of AS/RS is creating the need for computerized control algorithms to support the scheduling and picking decisions. This research addresses an order picking problem in a multi-aisle automated warehouse, in which a single storage/retrieval (S/R) machine performs storage and retrieval operations, and each item can be found in several storage locations. Our objective is to propose algorithms that minimize the total time traveled by the S/R machine to complete the retrieval process of orders. We develop a genetic algorithm and an ordinary heuristic, and provide a performance comparison of them with optimal solution. Numerical results from a large set of problems are reported.