The method of isonymy to estimate inbreeding is applied to the historical population of the Quebrada de Humahuaca . Data from the baptismal records of the Parochial Church of Humahuaca from 1734 to 1810 were grouped into two periods, 1734–72 and 1773–1810. The analysis was carried out twice: using the surnames exactly as they were registered; combining homonymous surnames which were pronounced or spelt in a similar way. The random and non-random components of inbreeding have been investigated through different methods. (...) There were no significant differences between the results of the two analyses, nor between the expected and observed isonymy. The value of Flies somewhere between those for offspring of first cousins once removed and second cousins once removed. There is a tendency for F and its components to increase through time. It is concluded that the high altitude aboriginal population of Humahuaca Parish must have behaved as a panmictic unit. (shrink)