Frozen hydrogen and deuterium pellets were injected into ohmically heated and additionally electron cyclotron resonance (ECR) heated plasmas of the TFR tokamak at Fontenay-aux-Roses. Without ECRH, the pellets penetrated deeply into the plasma and the ablation clouds were striated. The neutral gas shielding model predicts deeper penetration than was observed. The radial ablation profiles can be simulated by the Parks/Turnbull formula when a slightly stronger electron density dependence is assumed than is predicted by this original model. Pellet injection during ECRH led to increased ablation in the outer plasma region and in the limiter shadow. The position of the ECR layer had practically no influence on the pellet penetration depth, which was reduced to a few centimetres. Only two-thirds of the pellet mass were found as ionized matter in the plasma, compared to the Ohmic case. On photographs the ablation clouds showed no particular structure when ECRH was applied. Also the Hβ intensity was generally free of modulation. The increased ablation during ECRH can be simulated by an expression of the form given by Parks and Turnbull when one assumes two groups of electrons — the one representing the electrons of the bulk plasma and the other being a 'hot' electron gas of low density heated by the EC waves. There is strong indication that the 'perpendicular' temperature of this group is by orders of magnitude larger than its 'parallel' temperature. By using the 1-D transport code MAKOKOT it was possible to simulate the electron density evolution when suitable values of the anomalous radial convection velocity were chosen.