The concept of structuring complexity is described as a process in which, during medical investigation, intensity of laboratory examination is escalated as the perceived complexity of diagnostic need increases. Application of this concept to laboratory controlled testing protocols is discussed. A clinical chemistry protocol for thyroid testing of ambulatory care patients in British Columbia resulted in a 15% reduction in test use and a 12% reduction in laboratory charges to the third party paying agent over a two-year period. The need to develop medically acceptable laboratory protocols that encourage selective test utilization and reduce cost is emphasized.