From the roots of Uncaria tomentosa six oxindol alkaloids have been isolated and identified as isopteropodin, pteropodin, mitraphyllin, isomitraphyllin, rynchophyllin and isorynchophyllin. By ion pair chromatography on HPLC a fingerprint analysis has been worked out which allowed to differentiate between various Unicaria-species and drug preparations. With the exception of mitraphyllin and rynchophyllin all alkaloids showed a pronounced enhancement effect on phagozytosis, determined in two in vitro tests and the in vivo-carbon clearance test.