We have used commercially available molecular sieves (zeolites) to adsorb radioactivity onto small (approximately 2.1 mm diameter) beads for use in various applications in nuclear medicine. Soaking the beads in [99mTc]-NaTcO4 solution of approximately 3 GBq ml(-1) for 1-2 min can produce point sources containing 3-6 MBq total. Radioactive uptake was strongly dependent on bead size. We have employed the sources for gamma camera uniformity and as point source markers for interactive identification of anatomical landmarks. Due to their small size (<< system spatial resolution), relatively high uptake and negligible scattering contribution they provide excellent devices with which to measure spatial resolution, detector uniformity and energy resolution. The molecular sieves are inexpensive and readily usable with both single photon and positron emitting radionuclides.