1. The effect of T-2 toxin on active sodium transport across frog skin both in the presence and in the absence of stimulants of sodium transport, such as Amphotericin B and ADH, was studied using the short circuit current technique with the following results. 2. T-2 toxin produces inhibition of active sodium transport in a dose-response correlation. 3. This effect is irreversible since the washing out of the tissue does not restore its functionality. This indicates that the micotoxin may cross the cellular membrane and act on the internal site. 4. ADH partially removes the inhibitory effect of T-2 toxin. 5. The increase of the sodium pool in the cell as determined by Amphotericin B does not reverse the inhibitory effect of T-2 toxin. 6. The biological significance of these data is discussed in regard to the possible effect of T-2 toxin on Na+, K+-ATPase activity either directly or by a reduction in the metabolic supply of substrates, or by a modified stoichiometry of the pump reaction.