This paper presents high-quality CCD spectra (obtained at spectral resolving power =D % 2000) of the region surrounding the diffuse interstellar band (DIB) centered near 4428 Å , in some 35 O and early B stars located in the Cyg OB2 association. The reddenings of the stars range from EðBÀV Þ % 1:0 to 2.5 mag, allowing us to study the properties of the feature at high extinction, as compared with previous studies of DIBs in diffuse clouds. To our knowledge this is the first significant survey of

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... the 4428 Å DIB profile to be based on CCD-quality spectra, allowing us to probe the properties of this feature with high accuracy. Among our conclusions are (1) the profile of 4428 is symmetric and invariant within the uncertainties; (2) there is no clearcut dependence of band properties on stellar spectral type; (3) the equivalent width of the 4428 Å DIB as a function of increasing extinction appears to level off at around EðBÀV Þ % 1:0; (4) there is no evidence for emission wings associated with 4428; and (5) within the uncertainties the profile of the feature is fitted perfectly by a Lorentzian function, strongly suggesting that the band is broadened by natural damping. We conclude that the feature is created by rapid internal conversion in a molecular carrier.