A series of microcalorimetric experiments were performed to investigate the effect of La(3+) on the formation of the competent state of Escherichia coli HB101 by using a LKB-2277 BioActivity Monitor at 37 C. The thermogenic curves in the absence and in the presence of La(3+) were obtained. Based on these curves, we calculated that the total heat effects (Q(T)) and the maximal power (P(max)) in the presence and absence of La(3+). Our experiments indicate that the total heat effects in the presence of a low concentration of La(3+) (</= 100 microg/mL) are greater than those in the absence of La(3+). Their trends are similar with respect to the increasing concentration of La(3+). To the contrary, when the concentration of La(3+) is greater than 100 microg/mL, the total heat effects decrease with the increasing concentration of La(3+). Therefore, in the latter case, La(3+) has inhibitory effects on the formation of competence. Our experimental results suggest that the La(3+) ion in the environmental ecosystem can facilitate the formation of competence of E. coli HB101 and further stimulate the transfer of genetic materials between organisms.