In 240 patients the radioimmunosorbent (RIST) and paper-radioimmunosorbent (PRIST) tests were used parallel for determination of serum IgE levels. Whilst the values achieved with PRIST generally were somewhat lower than those with RIST, a very good correlation was found between these two methods. Taking its procedural simplicity into account, PRIST thus appears better suited for routine diagnostic purposes than RIST.