The objectives were to describe the systemic signs during the acute phase of experimental Escherichia coli mastitis and to relate these with losses in milk production during the reconvalescent period. Eleven cows, 20 to 30 d postpartum, were inoculated with 10(4) cfu of E. coli O157 in rear quarters. Heart rate, rectal temperature, frequency and amplitude of rumen contractions, plasma Zn and Fe concentrations, and counts of E. coli were used to monitor severity of disease during the acute phase. Areas under curves of clinical parameters, plasma Zn and Fe concentrations, and counts of E. coli were calculated during 36, 120, and 125 h postinoculation, respectively. Areas under curves of milk production were calculated during 21 d postinoculation. Losses in total daily milk production were related positively with areas under curves of heart rate, rumen amplitude, counts of E. coli in secreta from inoculated quarters, and plasma Zn and Fe concentrations. These parameters may prove suitable to establish an accurate prognosis for returning to milk production cows suffering from acute or peracute E. coli mastitis and to evaluate efficacy of drugs in experimental mastitis.