The γ-rays resultiing from Coulomb excitation of Pb 204, Pb 206, Pb 207 and Bi 209 have been measured in coincidence with the backwards scattered projectiles. The experiment was performed with α-particles accelerated to 20 MeV in a cyclotron. Reduced E2 transition probabilities have been obtained from the thick target γ-ray yields, and the errors whic may be involved in this procedure are discussed in some detail. For the single-particle transitions in Pb 207 and Bi 209 we have compared the observed E2 transition rates with the theoretical single-particle values calculate by Wahlborn for the case of a diffuse nuclear potential. The results indicate an effective E2 neutron charge of (0.85±0.20)· e in Pb 207 and an effective E2 proton charge ⪅2.6 e in Bi 209. The results for Pb 204 and Pb 206 have been compared with the predictions of Kisslinger and Sorensen. The agreement is good if one uses an effective E2 neutron charge of 1.0 e in these two cases.