The determination of the effective temperature of each individual star requires observations of the flux distribution in the largest possible wavelength range. Unfortunately, owing to observational constraints, this requirement severely limits the number of stars for which the direct determination of Teff can be achieved. However, an estimate of Teff for a very large number of stars can be obtained through a calibration of a photometric index versus the stellar effective temperature. The UV-Visual dereddened index, R=log(F 1965/F 5445), has been shown to be suitable for “normal” non-supergiant stars in the spectral type range B5 - F7 (Malagnini et al. 1984). The analysis, with the method described in Malagnini et al. (1983), of stars in the spectral type range B5 - B0, enables us to extend and to refine the already proposed calibration of R versus Teff. By using the complete calibration, the determination of Teff for all the “normal” non-supergiant stars sampled from the 31215 objects in the Catalogue of Stellar Ultraviolet Fluxes (Thompson et al. 1978) is being carried out.