Infrared (JHKLM) photometry of β Per, due to Zeilik (1980), has been analysed by computer-based optimization methods. The data have been used primarily to find empirical mean flux ratios at known IR wavelengths for the two photospheres of the eclipsing pair. These flux ratios have then been compared with values predicted by various model atmosphere calculations. The ratio of effective temperatures can be given asT B/T A=0.42±0.02, but there remains some small discrepancy between the empirical results and model calculations at the longest wavelengths (KLM). The possibility of ‘IR-excess’ at longer wavelengths is considered, but the evidence is marginal.