Two new sesterterpenes, thorectandrol A (1) and B (2), were isolated from extracts of the marine sponge Thorectandra sp. The structures were determined by extensive NMR spectral data analysis. NOE correlations were used to define the relative stereochemistry of 1 and 2, while CD data were used to suggest their absolute stereochemistry. Both compounds 1 and 2 inhibited the growth of MALME-3M (melanoma) and MCF-7 (breast) cancer cell lines in the range 30-40 microg/mL. The known compound palauolol (3) was isolated as well and was also cytotoxic.