Radioimmunoassay (RIA) has been used in the analysis of digoxigenin glycoside contents of crude ethanolic extracts prepared from fresh leaf samples of Digitalis lanata Ehrh. The commercial antidigoxin antiserum used in the assay was highly specific against the digoxigenin aglycone. Steroid derivatives with only slight structural differences from digoxigenin remained practically unassayed. The method is highly sensitive, and excellent values for accuracy, precision and correlation were obtained. Digoxigenin glycoside levels of second-year D. lanata leaves were found to be considerably higher than those of frist-year leaves.