Transport of lactic acid in supported liquid membranes containing tertiary amines (Alamine 336, Henkel Corp.) as the carrier was investigated. Both equilibrium extraction constants (K(t)) and effective diffusion coefficients (D) of the acid-amine complex were measured for systems with various diluents. Larger K(t) values and, thus, more efficient extraction were found when diluents were used, especially with oleyl alcohol which improved the polarity of the oil membrane and led to an approximately sixtyfold increase in the K(t) value. Experimental results of D for different supported liquid membranes were found in the range of 2 to 7 x 10(-7) cm2/s. Although much lower than those predicted by the Wilke-Chang equation, the values are consistent in the orders of magnitude with the literature results for other permeates in similar supported liquid membranes.