We have assessed the multiple biological variables on breast carcinoma FNA specimens using a Cytoblock technique. The growth fraction (MIB1), oestrogen receptor (ER), progesterone receptor (PR), p53 mutant protein, c-erbB-2, epidermal growth factor receptor (EGFR), NCRC11/epithelial membrane antigen (EMA) and DNA plopidy were examined. Objective quantification using image analysis (CAS 200) was applied as appropriate. Fifty cases were examined in this preliminary study. Excellent correlation between the Cytoblock preparations and parallel tissue sections was seen. Of the cancers, 81% were aneuploid with only 19% diploid in character, but 67% of the carcinomas were of histological grade 3. The mean nuclear area staining with MIB1 was 31.3% and with ER was 26.7%. Twenty-four percent (24.1%) of the nuclear area showed immunoreactivity with PR. Significant EGFR and EMA, respectively. A significant association between histological grade of the resected tumours and both MIB1 (P = 0.04) and EGFR (P = 0.02) expression in the Cytoblock samples was seen. p53 (P = 0.03) and EGFR (P = 0.01) immunoreactivity showed an association with tumour size. EGFR (P = 0.04) immunostaining also showed a relationship with the lymph node status of the patient. The technique is, we believe, a useful one for the assessment of multiple variables on breast cytology specimens; these preliminary data suggest that some of these may be useful in predicting prognosis in breast cancer patients.