Because La-138 is rare, refractory, and of peculiar nucleosynthetic origin, we have attempted to search for La isotopic anomalies hoping to find evidence for an early solar irradiation and clues for the astrophysical source of this nuclide. Whole rock samples from six meteorites and two terrestrial standards were measured using our newly developed analytical method. No anomalies could be definitively established. Our 95% confidence interval of 0.8 permil limits any differential proton fluence exposure to < 10(19)/cm2. Our limit implies either that the putative irradiation was uniform or that the mixing between irradiated and unirradiated matter was highly efficient on our sampling scale. This result contradicts the prediction of the model of LEE ( 1978) which was proposed to account for the production of both Al-26 and pure O-16 by proton irradiation. In general, our experiment does not support models for the production of Al-26 inside the solar system but a more direct test still awaits the analysis of La from Ca-Al-rich meteoritic inclusions containing different amounts of Al-26. La-138 excesses of about 1.2 permil in carbonaceous chondrites Murchison and Allende were found but these marginal (three standard deviations) effects require further confirmation.