Summary Yearly average conception rates (60- to 90-day non-returns) for 164 Holstein, 72 Jersey and 117 Guernsey sires were studied with respect to repeatability ( r ) and effect of age. The repeatability of single records of conception rate was found to be 0.59 for Holsteins, 0.45 for Guernseys and 0.31 for Jerseys. No uniform change in conception rate associated with advancing age was found. The failure to find a significant age trend in the conception rate of bulls at ages ranging from 2 to 13 yr. does not necessarily indicate that advancing age does not lower fertility. It does indicate, however, that it is possible to select bulls with high conception rates at all ages, ranging from 2 to 13 yr., inclusive, and that the influence of adding 1 or 2 additional years to the age of such bulls was not of sufficient magnitude to measure. This lack of significant change also was true over a period of 5 yr. for the 12 bulls which were kept that long.