During the course of a search for biologically active constituents from unexamined plant sources, several biogenetically interesting new di- and tri-terpenes and steroids were isolated from several weeds and shrubs of Euphorbiaceae and the bark, leaves and cones of several Pinaceae trees which had been treated as wastes in the forestry industry. Euphorbia supina contained 3,4-seco-5 alpha- and 5 beta-adian-4(23)-ene-3,5-diols and related oxides, oxygenated fern-8-en-3 beta-ols named supinenolones A-E and unusually migrated oxyfernanes having (9S)- and (9R)-7(8-->9)abeo-9-D:C-friedo-B':A'-neogammacerane skeletons named spirosupinane and neospirosupinane, while E. chamaesyce contained 3,4-seco-oleana-4(23), 18-dien-3-oic acid, 3,4-seco-8 beta H-ferna-4(23),9(11)-dien-3-oic acid and two oxygenated obtusifoliols. The bark of Phyllanthus flexuosus (Euphorbiaceae) contained 11 beta-hydroxy-D:A-friedo-olean-1-en-3-one, lup-20(29)-ene-3 beta, 15 alpha-diol, olean-12-ene-3 beta,15 alpha-diol and olean-12-ene-3 beta,15 alpha,24-triol together with trichadenic acid B for which we revised the structure to 3 beta-hydroxy-D:A-friedo-oleanan-27-oic acid. Two 26-nor-D:A-friedo-olean-14-enes were isolated from P. watsonii. Regarding Pinaceae trees, an unusually migrated abieslactone [(3R, 7S, 9R, 23R)-7-hydroxy-3-methoxy-8-oxo-7(8-->9)abeo-lanost-24-eno-26,23-lactone], named spiroveitchionolide, was isolated from the bark of Abies species, besides nine abieslactone analogues. Two pairs of unusually migrated serratanes, piceanonols A and B and jezananals A and B having novel skeletal systems of 14(13-->12) abeo- and 16(15-->14) abeo-serratanes named piceanane and jezanane, respectively, were also isolated from the stem bark of Picea species, besides three 14 beta,15 beta-epoxyserratanes and two 13 alpha,14 alpha-epoxyserratanes. The leaves of Larix kaempferi contained two deformed abietanes named karamatsuic acid (9,10-seco-9,10 alpha-epoxyabieta-8,11,13-trien-18-oic acid) and larikaempferic acid [9 alpha,13 alpha-epoxy-8-oxo-9(8-->7)abeo-7 beta-abietan-18-oic acid], as well as the cones to contain 8 alpha,12 alpha-epidioxy-15-hydroxyabiet-13-en-18-oic acid, three diepoxy-abietan-18-oic acids and two new dehydroabietic acid analogues. Several of the above compounds exhibited inhibitory effects against tumor-promoting and DNA topoisomerase II activities.