A number of new synthetic orthopaedic splinting materials, all claiming substantial advantages over the traditional plaster-of-Paris, have been introduced in recent years. However, although their properties have been extensively measured in the laboratory, little has been documented concerning their performance in clinical use. This study was therefore initiated as a comparative evaluation of the clinical characteristics and ease of use of these relatively expensive materials in the fabrication of below-knee weight-bearing casts. The study encompassed nine materials--seven based on water-activated polyurethanes, one thermoplastic and plaster-of-Paris, and involved a total of 203 patients. It was concluded that plaster-of-Paris should be used for all routine splinting applications, but that in cases in which cast weight, cast bulk, or the time to bearing weight is important, a synthetic material, chosen principally on the basis of cost, is indicated.