The effects of lanthanum doping on the transport properties and oxygen exchange kinetics of La-x(Ce0.9Pr0.1)(1-x)O2-delta (x = 0, 0.1 and 0.2) have been investigated by electrical conductivity on bulk samples and optical relaxation on thin films respectively. Lanthanum substitution was observed to increase the magnitude of ionic conductivity to values comparable to that of single substituted LaxCe1-xO2-delta, with a maximum for a La content of x = 0.1, reaching sigma = 9.5 x 10(-3) S.cm(-1) at 600 degrees C and a decrease in activation energy from approximate to 1 eV for Ce0.9Pr0.1O2-delta down to approximate to 0.75 eV for the lanthanum substituted compositions. At the same time, a significant electronic contribution to the total conductivity, estimated to be on the order of 10%, supports significant mixed ionic-electronic conductivity. Substitution with lanthanum increases the absolute values of the oxygen surface exchange coefficient from k(chem) = 6 x 10(-7)cm.s(-1) for Ce0.9Pr0.1O2-delta to k(chem) = 1 x 10(-6) cm.s(-1) for La-0.2(Ce0.9Pr0.1)(0.8)O2-delta at 550 degrees C. Moreover, one observes significant increases in activation energy from 0.7 eV for Ce0.9Pr0.1O2-delta to approximate to 1 eV for La substituted compositions, suggesting a change in the rate-limiting step. Possible sources for the change in the rate-limiting step are suggested. The composition with the highest La content of x = 0.2, although not exhibiting the highest ionic conductivity, shows the highest surface exchange rates, is suggested to result from enhanced segregation of catalytically active lanthanum to the surface.