We have measured the AC magnetic susceptibility of single crystals of the heavy fermion compounds CeCu6 and CeNi at temperatures down to 250 mu K. The susceptibility of CeCu6 shows a peak at about 2 mK in a zero magnetic field. The peak height along a-axis is about 10 times as large as along b- and c-axis, and decreases to zero in increasing field up to 11 mT. It is likely that the susceptibility of CeNi along c-axis has three peaks: below 350 mu K, at 47 mK and at 0.3 K, respectively. The two peaks at lower temperatures are suppressed by a magnetic field. The newly observed peaks in the susceptibilities for CeCu6 and CeNi suggest effects of magnetic impurities rather than of magnetic ordering. (C) 2000 Elsevier Science B.V. All rights reserved.