The present application describes sulfonyl-amidino-containing and tetrahydropyrimidino-containing compounds and derivatives thereof of Formula I: P.sub.4-P-M-M.sub.4I or pharmaceutically acceptable salt forms thereof, wherein M is a ring, P is an optional ring, and P.sub.4 and M.sub.4 are as defined below. Compounds of the present invention are useful as inhibitors of trypsin-like serine proteases, specifically factor Xa.