Hi list, I want to assign Metapost graphics to single letters (in a newly defined evironment, that take care of these assignments). The purpose is being able to rapidly build huge tables containing lots of these symbols. Everything works fine if I assign these graphics to non-letters, e.g. "|", but somehow it doesn't work with normal letters. Here is what I tried (with a simple Foo instead of Metapost graphics): \definesymbol[foosymbol][{\tt Foo}] \def\startmychars{% \bgroup\catcode`\|=\active\def|{\symbol[foosymbol]}} \def\stopmychars{\egroup} This works with | as reassigned character without any problems. But, we want to have normal characters in the table, no punctuation marks, etc. Does anyone know what to do to reassign a special definition for a letter e.g. like uppercase B or else? I got this error: (/usr/local/share/texmf/tex/context/base/pdfr-ec.tex) ! Undefined control sequence. \startmychars ...up \catcode `\B=\active \defB {\symbol[foosymbol]} l.24 \startmychars which seems to indicate that B is not recognized as active character in the "\defB"? Any hints very welcome, Enzo.