Technical Abstract: Limited information exists on the coupled release and transport of manure-borne fecal microorganisms and phosphorus (P) species in runoff. Under simulated rainfall, a study of the effects of live and dead grass on the release of Escherichia coli (E. coli), Enterococci, and various fractions of manure P was conducted in soil-grass runoff boxes. A general correlation was found between water-extractable P (WEP) and either bacterium released to runoff. However, the relationship between bacteria and WEP may be associated with the presence of colloids and suspended particulates in a clear runoff sample. A continuum of particle size was detected, and suspended particulates, ranging between 0.1 and 100 'm in size were present in runoff water throughout each simulation. In fact, the correlations of bacterium concentration to phytase-hydrolysable P (PHP), a fraction primarily associated with organic particulate manure, or to the more-inclusive total bioactive P or total P were higher than that with WEP. Therefore, E. coli and Enterococci have been released to runoff while associated with manure organic P particulates, and, the PHP forms in runoff may serve as surrogate indicator of fecal coliform and Enterococci release from grass-applied dairy manure.