DNA analysis in meningiomas was performed using flow-fluorescence cytometry in 71 tumours. Three subcategories of rather small, medium-sized or clearly abnormal growth activities were evident in each of the fibroblastic, transitional and syncytial tumour types. These categories reflected grades 1, 2 or 3 of malignancy on a four-grade scale in which the primary fibroscarcomas of the meninges are grade 4. Richly vascularized (haemangioblastic) meningiomas of our series comprised only two subcategories: these included 7 tumours with slight signs of proliferation and 1 with increased growth, probably indicating a propensity to recur. Tumours of grades 2 and 3 have a tendency to recur, which is probably due more to their biological behaviour than to the efficiency of the surgical treatment. The most variable patterns of DNA distribution are detected in the so-called "anaplastic" meningiomas: some of them are microscopically polymorphous blastomas but show unimodal diploid karyograms, whereas the proliferative indizes, ranging between 1 to 15, were obviously indicative for slow-growing benign tumours. The majority of polymorphous and anaplastic meningiomas, however, are characterized by a rather abnormal tetraploidy or aneu/polyploidy not uncommon in a relapse. The corresponding DNA distribution was demonstrated in a recurrent papillomatous meningioma in agreement with its dubious histological prognosis.