Past uranium mining in the area of Cunha Baixa village, near Mangualde (Portugal), led to contamination of subsurface waters used for irrigation in the agricultural area of this village. To test radionuclide transfer to plants, two side-by-side parcels of land, each divided into four replicate lots, were used for experimental growth of potatoes (Solanum tuberosum L.). One parcel of land was irrigated with water containing a high uranium concentration (13.7 Bq l−1) and the other was irrigated with water containing a low uranium concentration (0.3 Bq l−1). Agricultural procedures were controlled and radionuclide concentrations in soil and irrigation water were measured. The potato crop was collected and samples with and without peel were analysed for uranium isotopes (238U, 235U, 234U) and uranium series (238U daughters) alpha-emitting radionuclides (i.e. 230Th, 226Ra, 210Po). The results show a significant uptake of radium, reaching 12.9 ± 1.2 Bq kg−1 dry weight, and a minor uptake of other radionuclides by potatoes. Radium transfer to potatoes was enhanced in the parcel of land irrigated with water containing high radium concentrations, but radionuclide concentrations in irrigation water had a minor effect on the transfer of uranium, thorium and polonium to potatoes. Radionuclides were largely accumulated in tubers' peel and, in general, peeling removed most of the radioactivity. As radium in irrigation water was found to be accumulated in potatoes it may be transferred to man through the food chain. Therefore, this radionuclide should be monitored in agricultural zones near uranium mine areas.