Flow-injection analysis, founded on an approach that is entirely different from continuous-flow analysis, involves use of three principles: sample "injection," controlled dispersion of sample (rather than a dispersion retarded with gas bubbles), and reproducible timing. The conditions governing the dispersion of the sample in the flowing carrier stream are considered, and we illustrate how the dispersion can be manipulated to suit particular analytical requirements. Instrumentation and practical aspects of flow-injection analyses are discussed, especially with regard to clinical chemistry applications, and the technique is compared with the more conventional gas-segmented-flow analysis system. We conclude that, because of its speed, economy, and simplicity, flow-injection analysis will eventually replace the gas-segmented approach for many clinical chemistry analyses.