Rhodotorula mucilaginosa produces the siderophore rhodotorulic acid (RA) when grown in iron-limited conditions. R. mucilaginosa grew at rates between 0.10 and 0.19 h(-1) in iron-restricted conditions, depending on the carbon source, and at 0.23 h(-1) in iron-sufficient conditions. In bioreactors inoculated with iron-starved pre-cultures, initial specific growth rates in batch culture were dependent on the iron concentration. The critical dilution rate (Dcrit, at which steady state cultures cannot be sustained) in continuous cultures was also dependent on the iron concentration and was lower than mu(max) in batch culture. Sucrose was the best carbon source for RA production [287+/-11 micromol (g biomass)(-1)] and production could be further increased by supplementing the medium with the precursors acetate [460+/-13 micromol (g biomass)(-1)], ornithine [376+/-6 micromol (g biomass)(-1)], or both [539+/-15 micromol (g biomass)(-1)]. Citric acid was an effective suppresser of RA production. RA was produced in a growth rate dependent manner and was optimally produced at pH 6.5.