Mass transfer on single drops was studied experimentally, in a conical glass test cell on a laboratory scale. To determine the influence of internals on the mass transfer, two different sieve trays with hole diameters,of 3 and 6 mm, respectively, were inserted into the cell. In the experiments the resting times the drops stayed under and above a sieve tray were varied. Through the evaluation of the experimental results with a model, it is possible to determine the influences of the flow field and the sieve-tray passage on mass transfer separately. The mixing inside the drops while they passed through the holes is relatively small even if the drops are a little larger than the hole diameter. The influence of changes of the flow field caused by the sieve trays on mass transfer is larger and its quantitative magnitude depends on the system used.