Psammoclemma sp. (Phoriospongiidae) was selected for study through biological screening carried out in New Caledonia. The crude extract of Psammoclemma sp. was highly active on KB cells and its fractionation led to the isolation of two macrolides chondropsin A 1 and 73-deoxychondropsin A 2. The complex structures were elucidated by a combination of spectroscopic methods (NMR, ESI-MS/MS). These known compounds were evaluated for their cytotoxic activity towards several tumor cell lines and exhibited an IC50 of approximately 10(-10) M. Flow-cytometric analysis revealed that chondropsin A 1 and 73-deoxychondropsin A 2 blocked the entry of HL 60 and KB cells into G2/M phase, leading to cell death by apoptosis.