Using a thermal activity monitor (TAM) air isothermal microcalorimeter with ampoule mode, the thermo-genic curves of the metabolism of Tetrahymena thermophila BF(5) growth at 28 degrees C were obtained and the action of palmatine on it was investigated. Meanwhile, the biomass change during the process of T. thermophila BF(5) growth coexisted with palmatine was studied by a haemacytometer. The results showed that a low concentration (50 microg/mL) of palmatine began to inhibit the growth of T. thermophila BF(5), and when the concentration of palmatine reached 600 microg/mL, T. thermophila BF(5) could not grow at all. The relationship between the growth rate constant (k) and the concentration c was almost linear with the correlation coefficient of 0.9957, showing the strong toxic action of palmatine on T. thermophila BF(5) growth. The biomass during T. thermophila BF(5) growth decreased obviously by the addition of palmatine at different concentrations. The investigation of biomass agreed well with the results obtained by means of microcalorimetry.