Objectives. A main goal of neoadjuvant chemotherapy (CT) in locally advanced breast carcinomas (clinical size >3 cm) is to decrease the tumour volume to permit conservative surgery. In about 10% of the cases, the tumour nodule is not clinically palpable after CT and it is necessary to tattoo the initial site in order to guide the surgeon for the resection of any residual tumour. We have developed a charcoal suspension for injection into human breast tumours. The aim is to enable the pathologist to guide the surgeon during excision of the residual tumour, which is not otherwise visible, after CT. Pharmacological and toxicological studies in animals have indicated that the suspension is well tolerated. Methods. We investigated the efficacy and tolerability of a charcoal suspension in a group of eight patients with a palpable breast tumour of clinical size 1.5-4 cm, which was removed 24 hours to 4 days after the injection of 1 mL of 4% charcoal suspension into the tumour. Results. This preliminary clinical study shows that the injection of charcoal is well tolerated by patients and is a good method of tattooing tumour. The charcoal was seen in or at the periphery of the nodule in the surgical specimen. No inflammatory reaction or diffusion was observed. Conclusions. Based on these results, this suspension appears suitable for tattooing breast carcinomas over a period of 3 months for patients programmed to receive preoperative CT.