Compounds according to formula I: in which formula R1 and R2, which may be the same or different, represent halogen, (C1-C6) hydrocarbyl, optionally substituted with one or two hydroxyl group on one or more fluorine atoms, or, together with the carbon atom to which they are both attached, R1 and R2 form a (C3-C6)carbocyclic ring, or one of R1 and R2 taken together with R3 forms a direct bond, such that a triple bond is constituted, or R1 and R2 represent both hydrogen; R3 when not forming a direct bond with one of R1 and R2 represents hydrogen or (C1-C3)hydrocarbyl; X represents (E)-ethylene, (Z)-ethylene, ethynylene, or a bond; Y and Z independently represent hydrogen or methyl; the bond between C#16 and C#17 is depicted with a dotted line to illustrate that said bond may be either a single bond, in which case the projection of the ring substituents is beta, or a double bond; A represents hydroxyl, fluorine or hydrogen; B represents CH2 or H2; the configuration is the 3-position corresponds to the same configuration as in natural vitamine D3 (normal), or the configuration in the configuration in the 3-position is opposite to that of natural vitamin D3(epi); with the proviso that when X represents (E)-ethylene or (Z)-ethylene, one of R1 and R2 taken together with R3 may not form a direct bond, such that a triple bond is constituted; with the further proviso that when X represents a bond R1 ands R2 are nor hydrogen; with the further proviso that the compound of formula I is not 3(S)-hyroxy-9, 10-secocholesta-5(Z),7(E),10(19),22(E),24-penta-ene; and prodrugs and stereo isomeric forms thereof are provided together with their use in therapy, and their use in the manufacture of medicaments.