The application of a carbon fibre ultramicroelectrode (length 0.5 mm, diameter 8 mu m) to assess the impact of heavy metals on the eggs of two species of frog, the Xenopus laevis and the Rana sylvatica, was investigated. Coating mercury on carbon fibre electrode was found to improve the sensitivity and selectivity of the DPASV method. Using neutral buffer at pH 7 to simulate the frog’s egg for the determination of Zn, Cd, Pb and Cu, the working ranges were found to be : 0.1-5, 0.001-0.1, 0.05-0.2, and 0.05-1 ppm, detection limits 5, 0.3, 0.4, and 0.2 ppb, respectively, and repeatability 3.3 to 13% RSD. Using the standard addition method, Zn, Cd, Pb and Cu in the eggs of Rana sylvatica/Xenopus laevis were found to be 19/30, 0.5/0.5, 1.5/2.5, and not detected/1.2 ppb respectively. During environmental studies, Zn, Pb and Cd were enriched in the eggs, whereas Cu was found to be decreased. The concentrations of heavy metals were observed to decrease upon longer exposure time and at a higher temperature. The enrichment factors were found to decrease at higher metal concentration, indicating a reduction in the uptake of heavy metals at higher concentrations. The pH of the exposed solution was found to affect both peak current and potential and thus the pH of the exposed solution was buffered at 7. The carbon fibre ultramicroelectrode coated with mercury was shown to provide a suitable tool for micro-environmental investigation and the frog’s egg an effective biological indicator to assess the impact of pollutants on the environment to take into account of the biological variation in exposure to heavy metals.