Heterogeneous telomerase activity in CD138+-enriched cells from patients with multiple myeloma. Telomerase activity (TA) was determined in myeloma cells from 183 patients. Monoclonal CD138 antibody was used to isolate myeloma cells with a purity of more than 95% from bone marrow of patients with active disease. Results were expressed as a percentage of activity in a neuroblastoma (NB) cell line standard. Results showed that TA ranged from 0% to 427% of the activity in an NB cell line standard and that approximately 36% of myeloma patients had TA levels less than 5%; 51% had TA levels between 5% and 100%; and 13% had greater activity than this highly telomerase-positive tumor (higher than 100%).