In methyl [5-methoxy-4-(4-methoxyphenyl) isochroman-3-yl]-acetate, C20H22O5, (I), and methyl [4-(2,5-dimethoxyphenyl)-8- methoxyisochroman-3-yl] acetate, C21H24O6, (II), the heterocyclic rings adopt half-chair conformations. The substituents at the 3- and 4-positions are in a trans configuration in both ( I) and ( II), being in an axial conformation in ( I) and in an equatorial conformation in ( II). The crystal structure of ( I) is stabilized by weak C - H...O hydrogen bonding, leading to the formation of an infinite three-dimensional network. Compound ( II) crystallizes in a chiral space group. This feature, which was also found in previously investigated isochroman derivatives, is related to the arrangement of substituents attached to the isochroman moiety.