The purpose of the present work was to evaluate the proliferative char
acter of polycythaemia vera (PV). Therefore, in 15 patients with diffe
rent stages of PV we assessed the level of CD34 positive (CD34(+)) cel
ls in peripheral blood and bone marrow, erythroid colony growth of bon
e marrow cells and plasma erythropoietin (EPO). The mean concentration
of CD34(+) cells in blood was significantly increased in PV patients
(9.0 +/- 11.2 x 10(3)/mL) compared to healthy controls (2.0 +/- 1.7 x
10(3)/mL). In aspirated bone marrow no such difference between PV and
control subjects was present. Six patients with splenomegaly and/or re
quirement for chemotherapy had significantly higher mean blood levels
of CD34(+) cells compared to the remaining PV patients. All PV patient
s presented EPO independent erythroid colonies. Three PV patients with
anaemia and long disease duration had high EPO levels.