The growth of Strteptomyces coelicolor in a complex medium containing yeast extract, malt extract and glucose exhibited a biphasic mode of biomass accumulation. The first phase was associated with rapid biomass formation, phosphorus utilisation and lack of pigment production. The second stage was marked by slower growth and pigment formation. The demarcation between these phases appeared to result from the depletion of phosphorus in the media, which in turn allowed the red prodigiosin-like pigment to be expressed. Biomass formation appeared to involve the accumulation of phosphorus in the cells reaching a maximum level of 3.7 % of the dry weight. The depletion of phosphorus provoked the increase in alkaline phosphatase activity, which in turn produced a transient release of phosphorus into the medium, presumably from stored cellular phosphorus. Although glucose was consumed during growth, it did not constitute the only carbon source as the appearance of significant amounts of ammonium ions in the broth indicated deamination of amino compounds.