Two new 26-membered macrolides, reidispongiolide A (1) and B (2). have been isolated from the New Cakdoniaa marine sponge Rekiivpmgia werulea mgen. n.sp. J&i and L&i and their sbwtmn ehdated. They are related to spbinxolidea previously isolated from an unknown audibranch sod later from the sponge Neosiphonia supersles 1 and 2 co-occurs with spbinxolide B (4) awl D (3). These macrolides exhibited potent cytotoxidty against vaticw homaa carcinoma cells. The isolation of cytotoxic marine sponge macrolides has been rapidly increasing. They have heen isolated from sponges of the genus Theonella '_ Halichondria l, Mycale 3, Japsis 4 and very recently from a Spongia SP.~, a Cinachyra spb. and Hyrtios altum '. Previously we described discovery of potent cytotoxic 26-membered macrolides, sphinxolides and its congeners sphinxolides B-D, in the New Caledonian sponge Neosiphonia superstes (fam. Phymathellidae)'. Continued investigation of New Caledonian marine invertebrates for bioactive metabotites resulted in isolation and structural elucidation of two new cytotoxic macrolides, herein named reidispongiolide A (1) and B (2). from the marine sponge Reidispongia coerulea (Demospongiae, Lithistida, Phymatellidae) n.gen. and n.sp.