Experimental investigation of noise generation in InSb infrared photodiodes is reported. Minimum noise occurs when the diode is biased to zero potential. Noise spectra taken on seven photodiodes determined the white noise level above 1 kc. The experimental value of white noise is compared with the noise induced by random fluctuations in background radiation. The photonoise is calculated from⟨i2⟩/&Dgr;f=2qIPHfor an equivalent noise generator. The photoinduced currentIPHis measurable directly for zero bias potential. The total measured white noise is of the order of one decibel above the calculated photoinduced noise. Thus the photoinduced noise is the primary source observed, and InSb photodiodes closely approach the ideal case of being background‐limited infrared detectors.