AbstractTo study the effect of acetate inhibition on the parameters of yield and maintenance for bacterial growth, Pseudomonas putida ATCC 23467 was grown in a minimal salts medium with acetate as the sole carbon source with limiting and with excess quantities of urea in the feed medium. The behavior of the chemostat cultures under sole acetate limitation results in low residual acetate present in the fermentation broth. These cultures can be described satisfactorily using the equation qs = D/Yg + m, i.e., the acetate is consumed only for growth and maintenance,. Those cultures in which urea was limiting or where urea was present in large excess contained significant amounts of residual acetate in the broth. For these cultures it was necessary to add a third term for acetate inhibition to the above expression.