ABSTRACT
A new determination of the distances of the young open clusters NGC 2244 and NGC 2264 is presented. It is based on distance moduli for individual OB-type stars in which the influence of the anomalous ratio of total to selective extinction, if any, is taken into account. A discussion is included, first, of the accuracy of the color-difference method compared to that of other current methods for determining R and, second, of the errors in the determination of the distances for clusters embedded in nonuniform H II regions. New photoelectric measurements (UBVRI and JHKLM), and new spectrophotometric data (IDS spectra) are presented for OB-type stars in these clusters as well as summaries of published photometric data. The locations in the H-R diagram of the program stars seem to suggest that these massive stars are on the main sequence, supporting the idea of continuous star formation.