In this paper we describe the production of acid phosphatase (ACP) by Fusarium venenatum A3/5 in phosphate-limited continuous flow culture at different phosphate concentrations, specific growth rates, and pH values. ACP production in F venenatum was repressed by phosphate, and was only fully de-repressed at phosphate concentrations below 0.02 mM in the culture. The ACP was active from pH 2 to 7, and the activity could be attributed to one or possibly two isozymes, the one showing a strong activity maximum at pH 6, and the second showing a weaker activity maximum at pH 3. The specific ACP productivity was highest at dilution rates below D = 0.06 h(-1). ACP production was also influenced by pH, which showed two, clearly separated production maxima at culture pH 3.3 and 5.8. (c) 2006 Elsevier Inc. All rights reserved.