Lupus anticoagulant (LA), IgG and IgM isotypes of anticardiolipins (aCL), lipoprotein (a), and the resistance to activated protein C were determined in patients with ischemic stroke. The raised concentration of the aCL-IgM isotype was noted in 42% of patients with this type of stroke, and it was in contrast with an 8% frequency of an increased level of aCL-IgG isotype in these cases. The high level of lipoprotein (a) was found with similar frequency in stroke patients and in age-matched control subjects. It is concluded that the elevated concentration of IgM isotype of anticardiolipin antibodies can be regarded as significant in the ethiological work-up in elderly stroke patients.Copyright Lippincott-Raven Publishers