A long-standing rule of thumb for Phase III trials, provided they are well-designed and well-run, is that 50 percent come up positive and 50 percent come up negative. Friday was a case in point, as two major trials - of Amgen-Regeneron Partners' brain-derived neurotrophic factor (BDNF) and Amgen Inc.'s stem cell factor (SCF) - had negative and positive results, respectively.

Unfortunately, all clinical indications are not created equal, and the failure of the BDNF trial is much more important to the pocketbooks of both companies than the success of SCF is to AMGN's bottom line. Analyst estimates put the potential market for Regeneron Pharmaceuticals Inc.'s BDNF in amyotrophic lateral sclerosis (ALS) at $150-$500 million, and the potential for the compound in neuropathies at $1-$5 billion. In contrast, estimates for SCF are in the $15-$100 million range.