Optimal Hypotonic Solution is a newly formulated hypotonic solution which achieves maximum metaphase swelling (spreading) from difficult cells that are prone to either under-spread or over-spread, and where conventional hypotonic achieve inadequate cell swelling. Optimal Hypotonic Solution increases cell volume allowing the chromosomes more room to spread out. Well spread chromosomes with few cross-overs greatly facilitate analysis. Although developed for acute leukemia bone marrows and tumor specimens, it has also proved useful with problem blood harvests. Makes 1 litre of reagent