Active regions were followed across the disk on OSO 4 spectroheliograms in the Lyman continuum (LC) and in Mg x λ625. These observations indicate differential rotation with latitude, but not with height in the atmosphere. The measured equatorial sidereal rotation velocity is 14.7° ±0.2° per day in both chromospheric LC and coronal Mg x, where the quoted error is the standard deviation of a least-squares fit to the data.