%\hfill takes up all horiz space

\documentclass[10pt]{letter}
\signature{Dawn M. Nekorchuk}
\address{
Dawn Nekorchuk \\
70 Amherst St, \#149 \\
Cambridge, MA 02142 \\
(617) 225-1632 \\
dawneko@mit.edu}

\begin{document}
\begin{letter}{Ms. Cabasil \\                        
Human Resourse Director \\                       
Center for Pathobiology Research \\
49th Street \\
Someplace, MA  02359 }

\opening{Re: Microbiologist (research) position\\
Dear Ms. Cabasil,}

While exploring the website for Center for Pathobiology Research, I
noticed your announcement of a vacant Microbiologist (research)
position.  Please regard this letter as my formal
application. Enclosed is my resume showing my education, experience,
and background.

I am a recent graduate from Massachusetts Institute of Technology with
a Bachelor of Science in biology.  I have taken classes in immunology
and human disease.  Through the undergraduate research programs, I
have over a year of experience working in a toxicology laboratory.  

I would appreciate an opportunity to speak to with you to discuss the
Microbiologist (research) position and my future in the Center of
Pathobiology Research.  I am available for an interview and can be
reached at (617) 225-1632 or dawneko@mit.edu.  

Thank you very much for your time and consideration.

\closing{Sincerely,}

\end{letter}
\end{document}
