Heparin-induced thrombocytopaenia is a dreaded, although infrequent, complication of heparin therapy. We report two cases of heparin-induced thrombocytopaenia (HIT) type II occurring in a patient treated with standard (unfractionated) heparin and in another patient given a low-weight molecular heparin. The clinical course of the first patient illustrates the potentially severe thrombotic complications of HIT. Both cases were treated successfully by danaparoid sodium. Clues to the diagnosis and treatment are briefly discussed.