note Krambambuli If you run your code with perl -Dr (assuming your perl interpreter is compiled with debugging enabled), you'll see what I can see now too: the regexp engine works and works and works... However, I cannot see yet exactly what the solution is; at first sight, the regexp seems to be only extremely inefficient via the backtracks when it does _not_ find what it looks for. Update. A work-around to avoid the heavy backtracking when the wanted terms are not to be found in the wanted order might look like <code> if ($content =~ /$par2.*$par1/i) { if ($content =~ /\b($par2)(\W+(?:\w*\W*){1,$distance})?($par1)\b/i){ warn "IF 2"; my ($par1, $par2, $par3) = ($1, $2, $3); $content =~ s/$par1\Q$par2\E$par3/<$tag$class> $par1<\/$tag>$par2<$tag$class> $par3<\/$tag>/gi; } } </code> That works for me, but I guess there should be some nicer solutions too. Update2 Looks like using a regexp like <code> if ($content =~ /\b($par1)(\W+(\w+\W+){0,$distance})($par2)\b/i) { </code> works OK and also avoids the excessive backtracking for unsuccessful lookups. You'll have however to add an $4 and use it instead of $3 for the extra new match introduced with this. 841106 841341