The skin erythema meter is a fibre-optic, dual wavelength reflectance meter which measures the reflectance of the skin on two wavelengths, one the blood/haemoglobin absorption band (555 nm) and another a reference (660 nm). The instrument consists of a fibre-optic sensor head, a microprocessor-based control and analysis unit and a plotter, and it presents the relation between the measured reflectance results in terms of a reflectance index (R(555nm):R(660nm)). The measurement cycle, including printing, takes 5 seconds. Stability tests on the erythema meter (constant distance, reference object) showed the standard deviation of the reflectance index to be +/- 0.1%, while that in repeatability tests was <+1- 0.5% for skin and <+1- 0.2% for paper with hand-held positioning and repetition. The dynamic change in the reflectance index was about 30% with strong irritation. Results of various irritation test series on human skin are also presented. Finally, the performance and applicability of the skin erythema meter with respect to allergy test procedures, irritancy testing and measurement of UV-induced erythema are discussed.