Drawing on the similarities and differences between consumer and organizational search situations, this paper develops and tests a model of the professional buyer's external search for information. Key links between search effort and characteristics of the situation, the individual, and the organization are tested with a structural equation modeling approach. The data came from a sample of professional buyers involved in the purchase of a wide range of products. Results indicate that uncertainty surrounding the purchase plays a pivotal role in determining the amount of search effort expended. The importance of the purchase, however, and the organization's previous experience with the purchase are two main factors influencing that relationship. Marketing implications of these findings are discussed for industry practitioners. © 2001 by The Haworth Press, Inc. All rights reserved.