Thermal and potentiometric oscillations of Belousov-Zhabotinskii reactions catalyzed by Ce(IV) salt were simultaneously observed in a continuously stirred tank reactor. A heat exchange calorimeter of flow type was assembled. An Ag-AgBr electrode and one end of salt bridge were incorporated in the sample and reference vessels. Three kinds of stock solutions in 0.200 M sulfuric acid were used in typical runs, at concentrations of 0.420 M for potassium bromate, 0.900 M for malonic acid and 3.00 mM for ammonium cerium(IV) sulfate. Each reaction solution was introduced to the sample vessel of 50.86 cm(3) via three flow paths in the range of flow rate from 0.985-21.46 cm(3) min(-1) or of residence time tau from 3098 to 142 s. The total heat effect Q and the potential difference of bromide ions E in every oscillation were observed against time t and recorded on a Y-t recorder. Q (in Joules) was monotonously decreased with z and each oscillation cycle T-c of Q and E showed a maximum at z = 1053 s. The high period of E which corresponded to the heat evolving period was prolonged with decrease in tau. At tau = 144 s, irregular oscillations in cycle were observed. When all the components were concentrated twice, chaotic oscillations were obtained at z = 1053 s. By changing each concentration of four components to one half and twice, Q and E versus t curves were also observed.