The APACHE II severity of disease classification system was tested for its ability to identify intensive-care-unit (ICU) patients who would not benefit from treatment with total parenteral nutrition (TPN). First, the classification was validated in our patient population by testing it on 210 consecutive ICU admissions. Then a retrospective study was done on 89 ICU patients who had received TPN, to define APACHE II selection criteria. When the APACHE II system was tested prospectively on 26 ICU patients treated with TPN, it predicted correctly, with a specificity of 100%, half of the patients who died.