%Here are some definitions of mine that let you specify the indentation
%based on the width of the widest label, the way {thebibliography} does
%it; i.e., 
%\begin{labelpar}[def5678]
%\item[def1]...
%
% This is a style file, I guess labelpar.sty.
% It defines the labelpar environment as a list environment that looks like
% thebibliography.  There are two length parameters that you can change:
% \labelparsep and \labelparwid, which are analogous to \labelsep and 
% \labelwidth.  The \labelwidth can be changed by supplying the width of
% the widest label as an optional argument.  If no argument is given, the
% previous width is assumed.  The default width is the paragraph indentation.
% As it is written, the labels are left justified.  To change the label format,
% change the definition of \makelabel in \@@labelpar.
% 
\newdimen\labelparsep  \labelparsep .5em
\newdimen\labelparwid  \labelparwid\parindent \advance\labelparwid-\labelparsep

\def\labelpar{\@ifnextchar[{\@labelpar}{\@@labelpar}}

\def\@labelpar[#1]{\settowidth{\global\labelparwid}{#1}\@@labelpar}

\def\@@labelpar{%
  \list{}{\labelsep\labelparsep \labelwidth\labelparwid
  \def\makelabel##1{##1\hfil}% remove this line to right justify labels
  \leftmargin\labelwidth \advance\leftmargin\labelsep}}

\def\endlabelpar{\endlist\@ignoretrue}