Two series of 15,15-ethyleneacetals of PG F2α and PG E2 modified both in the α- and ω-chains were prepared with a view to find more stable and efficient analogues of this type. The synthesis of the analogues starting from the easily available (±)-[(3aα,4α,5β,6aα)]-5-(1,1'-biphenylyl-4-carbonyloxy)-4-formylhexahydro-2