Oestrogen (RE) and progesterone (RP) cytosolic receptors have been studied in 59 clinically inflammatory tumours of the human breast. The results were compared to those obtained in a series of 496 operable tumours. A single saturating dose of oestradiol for RE and R 5020 for RP was used and the cut-off between negative and positive tumours was 100 fmol/g tissue. A significant difference was seen (P less than 0.02) between the 2 classes of patients: (RE-, RP-) tumours were commoner among clinically inflammatory tumours (48%) than among operable ones (28%), independently of menopause. Concerning the histological type (based on an assessment of differentiation) and the histological grading (Scarff and Bloom) there was a significant difference (P less than 0.001) between the 2 populations of tumours. No significant difference was found in the distribution of RE and RP among the 3 histological types, whereas a significant correlation existed between histological grading and RE (P less than 0.02). Finally, patients with RE+ clinically inflammatory tumours constitute a lower risk group, especially when they are free of metastases at the time of diagnosis. The presence of RE therefore seems to indicate, as in the operable tumour group, a favourable prognosis.