Polymer-carbon black composites are a new class of chemical detecting sensors used in electronic noses. These composites are prepared by mixing carbon black and polymer in an appropriate solvent. The mixture is deposited on a substrate between two metal electrodes, whereby the solvent evaporates leaving a composite film. Arrays of these chemiresistors, made from a chemically diverse number of polymers and carbon black, swell reversibly, inducing a resistance change on exposure to chemical vapors. These arrays generate a pattern that is a unique fingerprint for the vapor being detected. With the aid of algorithms these patterns are processed and recognized. These arrays can detect and discriminate between a large number of chemical vapors.