Hello, I've misleaded you in my prev. letter: when I get TeX error with inputenc, I get an undefined control character, *not* an \IeC macro. This happens probably because this character gets to the TOC file translated, and when the TOC file is being read again, then the character gets translated again. And since there was no definition given tho that translated character, it defaults to \undefined. [This is probably, but I'm not 100% sure]. But why this error does not happen for AUX files? And why the second approach works correctly? Probably, this could be solved by using definitions like \DeclareInputText{"0F7}{\char130 } instead of \DeclareInputText{"0F7}{\CYRV} (because the definitions of russian letters in Babel package have the form \def\CYRV {^^82}). Anyway, it would be good to add functionality to inputenc package to declare character-to-character transliteration like the one used in the second approach (I mean a new macro like \DeclareInputCharacter). -- With best regards, Vladimir.