In an attempt to gain insights that might eventually lead to the development of new ways to avoid or minimize losses due to protein aggregation, we have performed dynamic Monte Carlo simulations on very simple lattice models of systems containing both isolated and multiple protein chains. Protein folding pathways, intermediate populations, refolding yields and aggregation were monitored as a function of both denaturant and protein concentrations. We find that there exists optimum levels of denaturant and protein concentration at which the refolding yield is highest, in agreement with some experimental observations.