The molecular phenotypes of ITI were analysed in samples from seven populations of the Iberian Peninsula (Galicia, Central Portugal, Castilla-Leon, Castilla-La Mancha, Extremadura, Western Andalusia, and Eastern Andalusia) by means of IEF in ultrathin layer polyacrylamide gels followed by immunofixation-silver staining. The observed ITI*3 frequencies exhibit the highest values thus far reported in European populations. Regression analysis between ITI*3 frequencies and latitude reveals a negative correlation (r = -0.8798, P < 0.001). © 1994 Wiley-Liss, Inc.