Aims: Studies were carried out to investigate the survival of Salmonella Typhimurium and Salmonella Derby in pig slurry during summer and winter seasons. Methods and Results: Pig slurry samples collected from a commercial fattening house were inoculated with a broth culture of Salmonella Typhimurium and Salmonella Derby, each at a level of log(10) 5 center dot 0 CFU ml) 1 and log10 2 center dot 0 CFU ml) (-1). At the higher inoculum level, S. Typhimurium and S. Derby survived for 34 and 23 days, respectively in the summer, and 58 and 46 days, respectively in the winter. Survival at the lower inoculum level for S. Typhimurium and S. Derby was 19 and 16 days, respectively, in the summer and 24 days for both in the winter. Conclusions: The survival of S. Typhimurium and S. Derby observed in this study indicates that a 2-month holding period of pig slurry, prior to land spreading, may be adequate if separate storage facilities are provided. Significance and Impact of the Study: Despite difficulties correlating laboratory studies with on- farm conditions, pig slurry may not represent a major source of transmission of Salmonella spp. in the farm environment in Ireland.