Hexadecafluoro zinc phthalocyanine (ZnPcF16), a second generation sensitizer for the photodynamic therapy of cancer, was incorporated in three vehicles: poly(d,l-lactic acid) (PLA) nanoparticles, polyethylene glycol (PEG)-coated nanoparticles and a Cremophor EL (CRM) oil-water emulsion. Nanoparticles were prepared by the salting-out procedure. Biodistribution of the dye was assessed by fluorescence in EMT-6 mammary tumour bearing mice after intravenous injection of 1 μmol kg−1 ZnPcF16. Plain nanoparticles were rapidly retained by the reticuloendothelial system (RES) as reflected by the low area under the blood concentration-time curve (AUC0–168, 57 μg h g−1). Little tumour uptake of the dye was observed with this formulation. In contrast, PEG-coated nanoparticles displayed a reduced RES uptake, leading to significantly higher blood levels over an extended period (t1/2 30 h; AUC0–168 227 μg h g−1) and enhanced tumour uptake. At 48 h post injection, tumour to skin and tumour to muscle concentration ratios reached 3·5 and 10·8, respectively. Blood levels of ZnPcF16 after administration as a CRM emulsion decreased faster than with PEG-coated nanoparticles (t1/2 12 h), but since no early liver uptake was observed, the AUC0–168 and the tumour uptake were only slightly lower. However, with the CRM formulation, a late liver uptake was observed, reaching 51% of the injected dose after 7 days.