The rapid degradation and subsequent lack of efficacy of n-butyric acid in vivo has been improved by the synthesis of monosaccharide stable pro-drugs of butyric acid. We studied the effects of D1 (O-n-butanoyl-2,3-O-isopropylidene-alpha-D-mannofuranoside), G1 (1-O-n-butanoyl-D,L-xylitol), and F1 (1-O-n-butanoyl 2,3-O-isopropylidene-D,L-xylitol) on the maturation and proliferation of AML cell lines HL 60 and FLG 29.1 and of purified blast cells from 10 cases of de novo acute myeloid leukaemia (AML). AML cell maturation was measured by surface antigen expression, morphology and cytochemistry. Toxicology in mice was also evaluated (DL50 1000 mg/kg). In HL 60 cells G1 and D1 increased the expression of CD15 and CD11a (presenting 62% of promyelo-metamyelocytes), and in 7/10 cases of primary AMLs that of CD11a, CD11b, CD15, and myeloperoxidase. D1, G1 and F1 induced a dose-dependent inhibition of tritiated thymidine uptake. Apoptosis (evaluated by flow cytometry and agarose gel electrophoresis) was induced in AML blasts by D1 and F1 (79% and 94% respectively for HL 60 cells) and, with less effect, by G1 (27%). The persistence of maturative and apoptotic activity in these new pro-drugs of butyric acid, hydrolysed only inside the tumour cell, suggests a possible use in differentiation therapy of myelodysplastic syndromes and AMLs.