Drug-induced immunologic thrombocytopenia, a fairly common disorder, is characterized by drug-dependent antiplatelet antibodies that destroy circulating platelets in the presence of the provoking drug or its metabolites. The development of reliable methods for the detection of platelet-bound immunoglobulins causing in vivo platelet destruction, such as the use of monoclonal antibodies tagged with fluorescein and flow cytofluorimetric analysis, has ushered in a new era to differentiate between immune and non-immune thrombocytopenias. A severe thrombocytopenia developed in an elderly female patient treated with tamoxifen, a non-steroidal anti-estrogen drug, after surgery for breast cancer. A tamoxifen-dependent platelet antibody was detected in the patient's serum and linked on the platelet membranes. This antibody reacted only in the presence of the offending drug and showed platelet specificity. Withdrawal of drug restored platelet count to normal levels.