The skewness of magnetic anomalies corresponding to chrons 25 to 32r (56--72 Ma) was investigated on 22 North Pacific profiles recording Pacific-Kula spreading. From 172 estimates of skewness we find that it varies with age, with irregular scatter superimposed on a steady increase with age of 1.20¿0.27¿/m.y. Skewness differs significantly between anomalies differing in age by as little as a million years. An analysis of the errors in the skewness estimates indicates significant errors that are systematic for an anomaly of a given age, but varying irregularly with age. The significant increase with age of phase shift may reflect an increase with age of anomalous skewness, or the northward motion of the Pacific plate, or both. If it is due entirely to Pacific plate motion, and an age-independent value of anomalous skewness of 14¿ found in prior studies is assumed, the rate of northward motion is 0.70¿0.26/m.y., four times faster than estimated from seamount paleomagnetic poles and paleolatidues determined from sediment cores. ¿ American Geophysical Union 1989