An ion microprobe has been used to observe 26Mg/24Mg in in excess of normal values in anorthite crystals from Allende refractory inclusions. In one crystal, 26Mg excesses up to 40% above normal, correlated with Al/Mg, were observed. These excesses are many times larger than those observed by other techniques. The correlation with Al/Mg indicated that the excess 26Mg in the Allende anorthite is uniformly distributed in the anorthite crystal. Analytical procedures and conditions were carefully controlled. Nevertheless, small but significant apparent 26Mg/24Mg anomalies in isotopically normal samples were observed in analyses by one ion microprobe. A repetition of the isotopic analyses using another ion probe produced normal ratios in the normal samples and confirmed large 26Mg excesses in the Allende anorthite.