This study compares the earth orientation results obtained by the NASA CDP and the NGS IRIS experiments. The results agree at about one combined formal error (two milliarcseconds) after small biases (one to three milliarcseconds) have been removed from each component. Furthermore the biases are found to correspond to small rotations between the reference frames, principally the terrestrial frame, for the two sets of experiments. In the past the CDP data has not been used in combined solutions of earth orientation parameters prepared by the data centers at the U.S.N.O. and the B.I.H. The authors propose that these data should be included because they are distinct from the IRIS data and represent an important supplement to those data. We also point out that the total number of observations is about equal in the CDP and IRIS experiment sets.