After refusing to sign a declaration of loyalty to Germany, he escaped from the occupied Netherlands via Switzerland to England, where he enlisted in the U.S.

[2] After World War II he worked in the laboratory of Prof. UG Bijlsma in the area of adrenergic substances and in 1950 both in the field of chemistry and medical doctorate.

Based on his dissertation, he developed together with Jacques van Rossum, a method for quantification of pharmacological effects as a result of ligand-receptor interactions.

An important accomplishment of Ariëns was the establishment of experiments on isolated organs instead of the living animal (ex vivo), which quickly and reproducibly delivered data on the affinity and intrinsic activity of test substances.

Ariëns was also active in the field of structure-activity relationships (SAR), a branch of medicinal chemistry.