The CDC25 phosphatases regulate the cell division cycle by controlling the activity of cyclin-dependent kinases. While screening for inhibitors of phosphatases among natural products we repeatedly found that some polyprenyl-hydroquinones and polyprenyl-furans (furanoterpenoids) (furospongins, furospinosulins) were potent CDC25 phosphatase inhibitors. These compounds were extracted, isolated and identified independently from three sponge species (Spongia officinalis, Ircinia spinulosa, Ircinia muscarum), collected at different locations in the Mediterranean Sea. The compounds were inactive on the Ser/Thr phosphatase PP2C-alpha and on three kinases (CDK1, CDK5, GSK-3), suggesting that some potent and selective CDC25 phosphatase might be designed from these initial structures.