Use of tetrahydrofolates in natural stereoisomeric form for production of a pharmaceutical preparation to influence homocysteine levels, to treat and prevent cardiovascular disorders and to prevent neural tube deficiencies is new. The compounds are applied when a methylene tetrahydrofolate reductase deficiency or thermolabile methylene tetrahydrofolate reductase exists. Tetrahydrofolates in the natural (S) form assist remethylation of homocysteine, and therefore act as homocysteine level modulators. They are of use in prevention and treatment of conditions in which there is deficiency of cystathione beta -synthase and/or 5,10-methylene tetrahydrofolate reductases enzymes. These conditions include cardiovascular disorders, notably arteriosclerosis, and for neural tube deficiencies. The compounds can be used either alone, or in combination with other bioactives, notably vitamins, and especially those of the B-group, B6 and B12, which have synergistic action.
