The concentration of c-erbB-2 oncogene-encoded protein (p185neu) in fresh tumour samples obtained at the time of surgery from 94 non-small-cell lung cancer patients (NSCLC) was determined by an enzyme immunoassay. The relative prognostic importance was estimated, and the influence of other predictors was assessed by means of a Cox's proportional regression model. Median concentration of p185 in tumour tissues was 206 U mg(-1) (range 21-1050 U mg(-1)). p185 level did not differ significantly among subgroups defined by TNM classification, histological type, sex and age. Categorization of patients by p185 level, with 206 U mg(-1) and 343 U mg(-1) taken as cut-off values (corresponding to the 50th and 80th percentiles of the frequency distribution), showed that the recurrence rate, cumulative disease-free likelihood at the 36-month follow-up and median time from surgery to the diagnosis of recurrence worsened progressively as the level of p185 increased. Multivariate analysis confirmed the independent prognostic value of p185 level. Risk of recurrence increased by 1.304 for every increase of 100 units in p185 concentration (95% CI 1.141-1.490) (P<0.001). These findings encourage the inclusion of p185 concentration assay in a future predictive multifactorial prognostic index in NSCLC.