Drug-induced immunologic thrombocytopenia, a fairly common disorder, i
s characterized by drug-dependent antiplatelet antibodies that destroy
circulating platelets in the presence of the provoking drug or its me
tabolites. The development of reliable methods for the detection of pl
atelet-bound immunoglobulins causing in vivo platelet destruction, suc
h 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 thrombocytop
enia developed in an elderly female patient treated with tamoxifen, a
non-steroidal anti-estrogen drug, after surgery for breast cancer. A t
amoxifen-dependent platelet antibody was detected in the patient's ser
um and linked on the platelet membranes. This antibody reacted only in
the presence of the offending drug and showed platelet specificity. W
ithdrawal of drug restored platelet count to normal levels.