The presence of c-erbB2, TGF-beta 1 and pS2 mRNAs was examined in primary breast tumours. The c-erbB2 mRNA was overexpressed in 34% of the tumours. There was a positive, statistically significant correlation between c-erbB2 gene overexpression and nodal status. TGF-beta 1 mRNA was detected in 84% of the tumours, regardless of their clinical status. When possible, the c-erbB2 and TGF-beta 1 proteins were identified immunohistochemically on frozen sections from the same tumours. For TGF-beta 1, the mRNA and immunohistochemical results were divergent in 6 cases, 5 of which did contain clearly detectable mRNA but did not stain with the antibody. The pS2 mRNA was detected in 22% of the tumours and in the BT474 cell line. There was a significant correlation between the presence of pS2 mRNA and of oestrogen receptors. No statistically significant correlation was observed between pS2 and TGF-beta 1 genes expression and the clinical parameters of the tumours.