In the free-radical addition of bisulfite to methyl 6-deoxy-hex-5-enopyranosides, which yields pairs of 5-epimeric methyl 6-deoxyglycopyranoside 6-sulfonates, it is found that proportionality exists between the ratios of 5-epimers formed and the relative conformational stability of the respective hex-5-enopyranosides ( e.g. 1) or the intermediary free-radical methyl 6-deoxyglycopyranoside 6-sulfonates ( e.g. 1a) formed during the addition reaction. Starting with five different methyl 6-deoxy-hex-5-enopyranosides, the ratios of glycopyranoside 6-sulfonates were determined by using 35S-labelled compounds; the differences in free energy were computed from these data. By means of the trial-and-error method, using known interaction energies and the measured differences in free energy between the pairs of diastereomers, new values for the absolute anomeric effect in methyl glycopyranosides have been calculated. The values (kcal/mole) are Δ −0.75 for OCH 3 axial-OH axial; −0.53 for OCH 3 axial-OH equatorial, +0.53 for OCH 3 equatorial-OH equatorial: and +0.75 for OCH 3 equatorial-OH axial. On the same basis, interaction energies for the glycosidic OCH 3 group were calculated as follows: with H (1,3-diaxial), +0.45; with OH (1,3-diaxial), +2.8; and with OH (1,2-gauche), +0.70. In the course of these studies, methyl 6-deoxy-6-iodo-α- d-galactopyranoside, methyl 2,3,4-tri- O-acetyl-6-deoxy-6-iodo-α- and -β- d-galactopyranoside, and methyl 2,3,4-tri- O-acetyI-6-deoxy-α- and β- l- arabino-hex-5-enopyranoside were synthesised.