BibTeX tries to enforce standard publishing rules regarding article titles and authors’ names; it sometimes changes uppercase letters to lower case. BibTeX also has trouble with umlauts, generally created in LaTeX with “{o}, because it is looking for the ” to end the input line. The general rule for overriding LaTeX’s and BibTex’s reinterpretation of your input text is to put the items you wish to be unchanged in braces. Thus, to obtain an umlaut in an author’s name or in an article title, or to force an uppercase letter, do something like the following:

@article{Kaczmarz37,
author = “S. Kaczmarz”,
title = “Angen{“{a}}hrte {A}ufl{“{o}}sung von {S}ystemen linearer {G}leichungen”,
journal= “Bull. Acad. Polon. Sci. Lett.”,
volume = “A35”,
pages = “355-357”,
year = “1937” }
This example shows the use of both umlauts and uppercase letters.