A comparison of spectroradiometric measurements has been completed for the wavelength region from 300 nm to 800 nm. The measurement procedures and results obtained in eighteen laboratories are described. The results are considerably better than those in earlier comparisons. Conclusions regarding procedures to be avoided are given. Without special precautions 45 degrees illumination on the diffuse receiver may cause serious errors. Normal illumination on a plane or a spherical receiver is better. The power in the spectral lines was inaccurately measured by Rössler's method.