note pvaldes <p>to grab the first 200 lines (each sequence having at least two lines) its a simple "head -n 200 myfile" problem or, if you want to be more perlish, while $my_file print if $. <= 200, but I suggest you to take a look to [http://search.cpan.org/dist/bioperl/|bioperl] in any case</p> 983938 983938