Many fundamental electrochemical investigations require accurate values of ionic or molecular diffusion coefficients. Such investigations are frequently carried out under conditions which do not satisfy the requirements of the Nernst expression l or the limiting laws ' -4 Hence diffusion coefllcients calculated from these latter . expressions may be in error whe; attempts are made to apply them to more realistic conditions. Only the tracer technique 5*6 has been shown to predict values of the diffusion coeff%zient which are in agreement with polarographic data'sa. Heyrovsky and K&a9 have discussed the feasibility of determining diffusion coefficients from polarographic data but most attempts at such determinations have met with only limited successloS1 '. Among the more successful attempts are those of Los and Murray'2*13 who derived a polarographic current equation For oscillographic methods. They concluded, and later demonstrated, that diffusion coefficients calculated by their expression from currents measured during the first two seconds of drop life should agree with corresponding tracer values. This investigation describes a simple method for the determination ofdiffusion coefficients by means of instantaneous polarographic current data from first drops. The results agree well with the corresponding tracer values. An iterative computer technique and an IBM 7094 computer were used to solve the Koutecky polarographic current equation for the diffusion coefficient. Special consideration has been given to the experimental satisfaction of the assumptions made in the derivation of the currenttime equation with special care given to the back-pressure effect and the problems associated with depolarization of the dropping mercury electrode. THEORY The electrochemical determination of diffusiori.cokffGents requires the USC of a satisfactory polarographic current expression. The Kouteckg equation14*1 ' is considered by many investigators to be the most rigorously derived polarographic current equation that considers spherical diffusion to a dropping mercury electrode.