Summary: We present the results of an experimental and numerical investigation of the effects of noise on pitchfork and Hopf bifurcations. Good quantitative agreement is found between calculations and experiment. In the case of the pitchfork we find that natural imperfections override the effects of the noise. However, novel noise amplification effects have been uncovered in the study of the Hopf bifurcation. These destroy the critical event found in the noise-free case and could be of considerable practical importance in systems containing dynamic bifurcations.