Among all metazoan phyla, sponges are known to produce the largest number of bioactive compounds. However, until now, only one compound, arabinofuranosyladenine, has been approved for application in humans. One major obstacle is the limited availability of larger quantities of defined sponge starting material. Recently, we introduced the in vitro culture of primmorphs from Suberites domuncula, which contain proliferating cells. Now we have established the primmorph culture also from the marine sponge Dysidea avara and demonstrate that this special form of sponge cell aggregates produces avarol, a sesquiterpenoid hydroquinone, known to display strong cytostatic activity especially against mammalian cells. If dissociated sponge cells are transferred into Ca(2+)- and Mg(2+)-containing seawater, they form after a period of two to three days round-shaped primmorphs (size of 1 to 3 mm). After longer incubation, the globular primmorphs fuse and form meshes of primmorphs that adhere to the bottom of the incubation chamber. Later, during incubation, freely floating mesh-primmorphs are formed. No bacterial rRNA could be detected in the primmorphs. We were able to prove that the primmorphs produce avarol. Levels (1.4 microg of avarol/100 microg of protein) close to those identified in specimens from the field (1.8 microg/100 microg) are reached. Avarol was extracted from the cells with EtOAc and subsequently purified by HPLC. The identification was performed spectrophotometrically and by thin-layer chromatography. Single cells apparently do not have the potency to produce this secondary metabolite. It is concluded that the primmorph model is a suitable system for the synthesis of bioactive compounds in vitro.