Catechins are polyphenols with antioxidant activity. The fruit Cocos nucifera (Palmae) has a fi ber husk rich in catechins and the local population of northeast Brazil uses it as a medicine against various diseases. An anti-bacterial and anti-viral activity has been already observed using this substance. Plant extracts, from other sources, rich in catechins are inhibitory to tumour cells, suppressing their proliferation. The aim of the present work was to verify if catechins isolated from Cocos nucifera were capable of inhibiting cell proliferation. An extract obtained from Cocos nucifera was purified through adsorption chromatography using the resin XAD-2. The purified material was used in cultures of an erythroleukaemia cell line (K562) and on normal human peripheral blood lymphocytes. Cell viability was assessed using MTT. Cellular proliferation was measured by [(3)H]-thymidine incorporation and cell cycle analysis in a fl ow cytometer. A dose-dependent inhibitory effect was observed on tumour cells and on lymphocytes activated by phytohemaglutinin (PHA) or phorbol ester. For PHA this effect was irreversible being already established on the fi rst four hours of culture.