The autoignition of butane has been studied by two techniques. At a relatively low pressure (1.8 bar), a two-stage flame has been fully described by following the stable-species and peroxy-radical evolution. At higher pressures, studies have been conducted in a rapid-compression machine in order to investigate the evolution of the autoignition delay times with temperature. These experimental results are compared with predictions obtained from a butane-oxidation model based on a complete mechanism of 133 species and 689 reversible reactions as proposed and tested at low pressure by Pitz, Wilk, Westbrook and Cernansky. In a reduced version (45 species, 272 reversible reactions) the model agrees with the measured major species produced in the second stage of a burner-stabilized two-stage flame. In its complete version, it also predicts the negative temperature coefficient observed at high pressure in the rapid-compression machine. However to account for the ignition delay, it was necessary to modify the rate constants associated with the low-temperature mechanism as suggested by Pitz, Leppard and Westbrook.