The potential of protoporphyrin IX fluorescence induced by the systemic administration of delta-aminolevulinic acid (ALA) for the detection of tumours was tested in three different murine models (MS-2 fibrosarcoma, L1210 leukaemia, and Lewis lung carcinoma). Time-gated fluorescence images were acquired up to 4 h after the intraperitoneal injection of ALA (200 mg (kg body mass (BM))-1). For comparison images were acquired also after the administration of 25 mg (kg BM)-1 of haematoporphyrin derivative. The latter drug was characterized by better localization in the tumour area, leading to higher fluorescence contrast between neoplastic mass and surrounding healthy tissue, and consequently was preferable for tumour diagnosis in all the models under study.