Single drops supported on hypodermic tubing have been studied in a wind tunnel to determine the effect of drop oscillation on mass transfer. The systems studied for the case where internal resistance controls consisted of absorption of SO2 gas by drops of glycerine, propylene glycol, and ethylene glycol. The results can be expressed in terms of effective diffusivity. The effect of oscillation on external mass transfer coefficients was studied by sublimation of naphthalene spheres. A technique has been developed for studying the effect of internal circulation on effective diffusivity, using forced circulation through a drop suspended on hypodermic tubing. A 'pseudo-film thickness' is determined as a function of circulation velocity, and presents a means of predicting effective diffusivity. This technique has been demonstrated for the system SO2-H2O, giving results in fair agreement with the correlation of Garner and Lane. (Modified author abstract)