Spectra of early-type stars in several heavily reddened OB associations are used to study broad diffuse bands in the range from 5700 to 6300 angstroms. The features at 5778 angstroms and 6170 angstroms correlated well with narrower lines in their vicinity. The 5795-angstrom band is not correlated with the overlapping line at 5797 angstroms but appears to be part of a structure which includes 5780- and 5778-angstrom features. The profile of the band at 6170 angstroms is smooth and featureless; the shape of the 5778-angstrom band is more complex with three well-defined peaks. The explanation for the observed correlation patterns can be found more easily within molecular theories of the origin of bands. It is shown that vibronic interactions in individual molecules or a superposition of narrower lines from slightly modified but closely related species can give rise to broad bands, such as 6170 and 5778 angstroms.