The effect of fat and non-fat dry matter (NFDM) of milk, and starter type, on the rheological properties of set yoghurt during the coagulation process was studied using a rotational viscosimeter. The pH was monitored simultaneously with viscosity readings. Recombined milk was cultured with yoghurt starter culture (YC), consisting of Streptococcus thermophilus and Lactobacillus bulgaricus, or ABT1, consisting of S. thermophilus, Lactobacillus acidophilus and bifidobacteria, at 40 degrees C until the pH dropped to 4.7. Yoghurt made with ABT1 had higher viscosity values than yoghurt made with YC. The NFDM content of milk had a major effect on the viscosity of curd made using YC or ABT1. For YC and ABT1, three stages were identified on the viscosity-incubation time curves and viscosity behaviour was different in each stage.