Abstract In an attempt to improve the predictive value of œstrogen-receptor measurements in breast-tumour biopsy specimens, œstrogen receptor was measured at both cytoplasmic and nuclear levels. Although 33% of patients had receptors at both levels, another 17% had cytoplasmic but no nuclear receptors. Theoretically, this latter group would not be expected to respond to hormone therapy. 7% had nuclear but not cytoplasmic receptors. The six-month follow-up data for the group of patients with receptors at both cytoplasmic and nuclear levels suggests qualitatively that this group has a good chance of responding favourably to hormone therapy. Much larger numbers must be accumulated before quantitative conclusions can be reached.