Abstract: The present invention describes novel 2,4-disubstituted 1,3-dioxolanes having the formula I ##STR1## wherein R.sup.1 represents a long chain alkyl group; X is a covalent single bond, a carbonyl group, a carboxyl group, a carbamoyl group or a --O--P(.dbd.O)(O.sup.z)-- group; z is a negative charge (-) when q is zero, or z is an hydrogen atom when q is one; n is an integer from 2 to 10; R.sup.2, R.sup.3 and R.sup.4 are lower alkyl groups, or R.sup.2 R.sup.3 R.sup.4 N.sup.+ represents an aromatic cyclic ammonium group or R.sup.2 R.sup.3 R.sup.4 N.sup.+ represents a non-aromatic cyclic ammonium group in which two of the groups (R.sup.2, R.sup.3 or R.sup.4) form a non-aromatic ring together with the quaternary nitrogen atom; and A.sup.- is a pharmaceutically acceptable anion. These compounds are in vitro inhibitors of the platelet aggregation induced by the platelet activating factor (PAF) and, thus, useful for the treatment of the diseases in which this substance is involved.