The present application describes lactam-containing compounds and derivatives thereof of Formula I: P.sub.4-P-M-M.sub.4I or pharmaceutically acceptable salt forms thereof, wherein ring P, if present is a 5-7 membered carbocycle or heterocycle and ring M is a 5-7 membered carbocycle or heterocycle. Compounds of the present invention are useful as inhibitors of trypsin-like serine proteases, specifically factor Xa.