A systematic procedure for the design of an enzymatic biosensor for body fluid analysis was developed. The sensor product attributes are first identified and translated into quantitative technical requirements. Components such as enzyme, indicator, and transducer, operating conditions such as pH, temperature, and enzyme amount, and the device configuration are then determined based on heuristics and databases. The detection performance is evaluated and improved to meet the technical requirements via an iterative approach guided by a causal table. The design procedure is illustrated with the design and development of a new lactate biosensor that shows excellent performance in testing saliva samples.