Six known lupanes lupenone ( 1), 3- epi-lupeol ( 2), glochidone ( 4), glochidonol ( 5), glochidiol ( 6) and lup-20(29)-ene-1beta,3beta-diol ( 7) were isolated from the roots and stem wood of Glochidion eriocarpum and three, 5, 6 and lup-20(29)ene-3alpha,23-diol ( 3), were isolated from the roots and stem wood of Glochidion sphaerogynum. Compounds were identified by (1)H- and (13)C-NMR techniques. Triterpenes 2 - 7 were tested against the growth of three human tumor cell lines, MCF-7, NCI-H-460 and SF-268. Lupanes 3, 5, and 6 exhibited strong inhibitory effects against all three; thus GI (50) values for 3 were 12.7 +/- 3.7, 17.9 +/- 1.1 and 17.9 +/- 0.5, for 5 9.0 +/- 3.7, 4.9 +/- 0.2 and 9.8 +/- 0.5, and for 6 6.63 +/- 0.7, 7.5 +/- 0.5 and 9.7 +/- 0.3.3. Epilupeol was less active, with GI (50) values of 75.6 +/- 11.7, 86.1 +/- 12.4 and 80.9 +/- 2.6 while 7 was moderately active only against MCF-7 (GI (50) = 79.2 +/- 2.4). Additional studies indicated that triterpenes 5 and 6 exerted their antiproliferative activity through the involvement of apoptosis while triterpene 3 did not.