Parathyroid hormone-related protein (PTHrP) 1-86 was quantified by immunoassay in extracts of 132 breast cancers, 27 samples of normal breast tissue and four fibroadenomas. PTHrP 1-86, was detected in 68% of primary tumours (range 40-302,000 fmol/g), 33% of normal breast tissues (range 100-1800 fmol/g), and all four fibroadenomas (range 110-11,600 fmol/g). PTHrP displayed molecular heterogeneity on gel filtration chromatography, and 1-86, 1-34 and 37-67 immunoreactivity eluted as 25-27 kDa together with a peak of 19-21 kDA containing only 37-67 activity. Tumour PTHrP 1-86 levels correlated inversely with age (P < 0.05) and were higher in premenopausal women (P = 0.05). The proportion of tumours containing PTHrP was higher in axillary node positive premenopausal women (P < 0.05). These data suggest that oestrogen may regulate expression of PTHrP in breast cancer and that production of PTHrP may be linked to development of axillary node metastases.