The intensity fluctuations in the emission from various lasing and nonlasing modes of a cw GaAs laser have been measured. The measurements were made by two techniques: the coincidence-counting version of the Hanbury Brown-Twiss intensity interferometer, and the single-detector excess-photon-noise technique. The two independent methods give excellent quantitative agreement. The intensity noise in the single lasing mode was studied as the laser was taken continuously through the threshold region; this has permitted observation of the gradual change in the statistical nature of the photon noise which occurs at laser threshold. Observations have also been made of correlations between the intensity fluctuations in the emission from different modes of the laser. The experimental observations of intensity fluctuations and correlations and their dependences on injection current can be understood in terms of the response of single or of coupled van der Pol oscillators to random-noise excitation. © 1965 The American Physical Society.