This study evaluated the potential role of L-(1-(11)C)-tyrosine positron emission tomography (TYR PET) for visualisation and quantification of protein metabolism in lung cancer. Dynamic TYR PET scans of the thorax were performed in 17 patients with lung cancer. Protein synthesis rate (PSR in micromol/min x l) and standardised uptake value (SUV, corrected for body measurements) of tumour tissue and contralateral normal tissue were calculated before and after chemotherapy or radiotherapy. All tumours [11 non-small cell lung carcinomas (NSCLCs), five small cell lung carcinomas (SCLCs), and one pleural mesothelioma] were visualised as a hot spot. The median PSR in tumour tissue was higher than that in corresponding contralateral normal lung tissue before [1.88 micromol/min x l (range 1.10-3.42) vs 0.40 micromol/min x l (range 0.12-0.86); P=0.003] and after treatment [1.33 micromol/min x l (range 0.45-2.21) vs 0.28 micromol/min x l (range 0.18-0.51); P<0.02]. In contrast to PSR of normal lung tissue, PSR of tumour tissue decreased significantly after therapy (P=0.03). Before therapy, no significant difference in PSR between NSCLCs and SCLCs was observed, but after therapy the PSR differed significantly between the subgroups [1.69 micromol/min x l (range 0.63-2.78) for NSCLC vs 0.67 micromol/min x l (range 0.45-0.92) for SCLC; P=0.03], irrespective of the treatment modality. The median SUV of tumour tissue was higher than that in corresponding contralateral normal lung both before and after therapy. Only a weak correlation between PSR and SUV was found when the latter was corrected for body surface area or lean body mass. Carbon-11 labelled tyrosine appears to be a good tracer for visualising lung cancer. PSR of tumour tissue can be used to quantify reduction in the metabolic rate of the tumour. Future studies need to be performed to determine whether TYR PET will supply additional clinical information with treatment implications in patients with lung cancer.