Abstract: Genetic properties of higher plants are transformed by incubating protoplasts of the plants together with plasmid DNA. The incubation is effected in the presence of polyethylene glycol and calcium ions. Subsequently--during after-incubation--the calcium ion concentration in the incubation medium is gradually increased and at the same time the polyethylene glycol concentration is decreased. The resulting aggregates are separated, grown further separately, and examined for modification of their genetic properties.