Production of poly(3-hydroxybutyrate) [P(3HB)] from whey by fed-batch culture of recombinant Escherichia coli CGSC 4401 harboring a plasmid containing the Alcaligenes latus polyhydroxyalkanoate (PHA) biosynthesis genes was examined in a 30 l fermenter supplying air only. With lactose below 2 g l(-1), cells grew to 12 g dry cell l(-1) with 9% (w/w) P(3HB) content. Accumulation of P(3HB) could be triggered by increasing lactose to 20 g l(-1). By employing this strategy, 51 g dry cell l(-1) was obtained with a 70% (w/w) P(3HB) content after 26 h. The productivity was 1.35 g P(3HB) l(-1) h(-1). The same fermentation strategy was used in a 300 l fermenter, and 30 g dry cell l(-1) with 67% (w/w) P(3HB) content was obtained in 20 h.