Conventional staging laparoscopy in combination with fluorescence diagnosis has proven to be an effective modality in the detection of macroscopically occult intraperitoneal tumours and metastases. Rats with induced peritoneal carcinosis are photosensibilized by intraperitoneal aminolaevulinic acid (ALA) lavage. After visualization of the tumour foci, the emission from the lesions is measured spectrometrically and the fluorescence analysed quantitatively ('optical biopsy'). There is a considerable accordance between imaging by fluorescence diagnosis laparoscopy and point spectrometry in the detection of peritoneal malignancies. Compared with surrounding healthy peritoneum, tumour-positive areas show significantly higher fluorescence intensities in spectrometry.