Theorem bodies printed in a roman font

If you want to take advantage of the powerful \newtheorem command without the constraint that the contents of the theorem is in a sloped font (for example, you may want to use it to create remarks, examples, proofs, …) then you can use the AMSLaTeX amsthm package (which now supersedes the theorem package previously recommended in these answers). Alternatively, the following sets up an environment remark whose content is in the default roman font.

\newtheorem{preremark}{Remark}
\newenvironment{remark}%
  {\begin{preremark}\upshape}{\end{preremark}}

amsthm.sty

Distributed as part of amslatex

ntheorem.sty

ntheorem

theorem.sty

Distributed as part of 2etools

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