Isolated immunomodulatory (e.g. immunostimulatory) polyhydroxlated pyrrolizidine compounds having the formula are disclosed. In these compounds R is selected from hydrogen, straight or branched, unsubstituted or substituted, saturated or unsaturated acyl, alkyl (e.g. cycloalkyl), alkenyl, alkynyl and aryl groups. The compounds are useful in therapy and prophylaxis, including increasing the Th1:Th2 response ratio, hemorestoration, alleviation of immunosuppression, cytokine stimulation, treatment of proliferative disorders (e.g. cancer), vaccination, stimulation of the innate immune response and boosting of the activity of endogenous NK cells.