The virulence of twelve Salmonella enterica isolates, seven serovar Typhimurium and five serovar Enteritidis was evaluated in vivo after oral, intramuscular and intravenous inoculation of chickens. It was assumed that the bacteria would exhibit different degrees of virulence according to their origin. The experiments were conducted in order to obtain a method to evaluate the virulence of field isolates of Salmonella in the chick, via a method, which is more rapid than conventional models. Results were obtained within 21 days for the oral model, considered to be the reference, and within 7 days for the intramuscular model. The classification achieved with the intravenous model, comparing either mortality results until seven days or bacteraemia levels at 48-72 hours, was identical. Thus, a bacteraemia model using 12-day-old chicks inoculated intravenously with Salmonella Typhimurium isolates allowed rapid assessment of their relative virulence. Moreover, the bacteraemia assays were used to test invA mutant strains of both serotypes and appeared useful in the differentiation between a Salmonella Typhimurium wild-type strain from the isogenic invA mutant.