This model evaluates the potential risk to humans from exposure to pathogenic microorganisms following land application of municipal sewage sludge. The five municipal sewage sludge management practices addressed by the model are: (l) application of liquid sludge for production of commercial crops for human consumption; (2) application of liquid sludge to grazed pasture; (3) application of liquid sludge for production of crops processed for animal consumption; (4) application of dried or composted sludge to residential gardens; and (5) application of dried or composted sludge to residential lawns. The various locations, states or activities in which sludge or sludge-associated pathogens exist are called compartments. They vary to some extent among practices. The computer model represents the compartments and transfers among compartments of the five management practices. In each compartment, pathogens either increase, decrease or remain the same in number with time, as specified by 'process functions' (growth, die-off or no population changes) and 'transfer functions' (movement between compartments). The population in each compartment, therefore, generally varies with time and is determined by a combination of initial pathogen input, 'transfer functions' and 'process functions.'