Aim: This study investigated the growth potential of Salmonella serotype Typhimurium and faecal indicator organisms in compost materials and the correlation between bacterial growth potential and the physico-chemical composition of the compost substrate and temperature. Methods and Results: Survival of Salm. Typhimurium, Enterococcus spp. and total coliforms at 14, 24 and 37 degrees C was determined in material of different degrees of maturity collected from composting plants for household waste and manure. All three micro-organisms showed the potential for growth in the material from active composts (Solvita index 4) but inactivation generally occurred over time in mature compost material (Solvita index 7-8). Conclusions: Salm. Typhimurium had the potential for growth in psychrophilic/mesophilic (P/M) zones of immature compost material and its growth potential correlated negatively with the maturity of the compost and the temperature within the simulated P/M zone. Significance and Impact of the Study: The risk of pathogen regrowth in P/M zones during organic waste composting further emphasizes the importance of good management practices and of avoiding P/M zones in combination with low compost maturity.