Biological screening of extracts of various bryophytes showed that the species Dicranum fulvum gave extracts with activity in both <u>in vitro</u> and <u>in vivo</u> bioassays. This plant was thus selected for extraction and fractionation, monitored by i<u>in vitro</u> bioassays. Isolation was guided by a combination of bioassay and chemical methods, and led to the isolation of three compounds, betulin, 9,l9- cyclolanostâ 23â eneâ 3,25â diol, and B-sitosterol. Purification was achieved by open column, flash column, gel filtration, thin layer chromatography, the chromatotron and crystallization. The isolated compounds were identified by comparisons of spectroscopic data with those of authentic samples and the matching of experimental and literature melting points and optical rotations. / Master of Science