Gallium-67 scintigraphy has been of limited use in detecting lung cancers and micrometastases. To study its potential for determining the aggressiveness of a cancer, we reviewed the charts of 44 patients with non-small-cell bronchogenic carcinoma who had not been receiving treatment when 67Ga scintigraphy was performed. The mean length of survival for the 18 patients with low or little uptake of the tracer, corrected for tumour size, was 19.7 months, and for the 26 with high uptake 9.4 months (p less than 0.01). Such in-vivo predictive assays may be a rational goal for tumour scintigraphy.