Transformation relations are derived for the conversion of Strömgren system colors for earlytype stars into equivalent Johnson system colors. The relation (U -B) = 0.675 (u-b) -0.938 is valid for O and B stars of all luminosity classes and A and F stars of luminosity classes III to V. The relation (B-V) = 1.584 (b -y) + 0.681 m 1 -0.116 is valid for O and B stars of all luminosity classes and A stars of luminosity classes III to V. No significant reddening corrections appear to be necessary

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... these relations, which are accurate to ± 0.016 and ± 0.022 in the transformed values of (B-V) and (U-B), respectively. Examples are given of color-dependent and magnitude-dependent effects in published UBV data. Such problems have important consequences for the distance scale of cluster Cepheids.