Differences in banding scales for milk quality penalties, as determined by bulk tank somatic cell count (SCC), prevent the use of a single economic value for SCC in an overall economic-genetic selection index (Veerkamp et al., 1998) such as, Profitable Lifetime Index or £PLI. But SCC could be used as a predictor of mastitis as genetic correlation estimates between mastitis and SCC are medium to high (review of Mrode and Swanson, 1996). This suggests that, although deriving a direct single economic value (EV) for SCC based on bulk tank SCC is difficult, a single financial value could still be assigned to SCC based on its relationship with mastitis. Here we use a genetic regression method to calculate the EV of SCC (EVSCC) as a predictor of mastitis. However, the dependency of regression coefficients on mastitis incidence (p) could make such EVSCC variable. The main objective of this study was to evaluate the impact of such relationship on EVSCC and genetic selection in dairy cattle using predicted transmitting abilities of SCC (PTASCC).