The present invention concerns a method of preparing pharmaceutical compositions of a biologically active proteins, in particular multicomponent interferon compositions. The invention comprises the steps of adding to a solution of the protein a non-ionic detergent in an efficient amount to provide an extended shelf-life of the pharmaceutical composition; subjecting the solution containing the non-ionic detergent to filtration on a virus removal filter with a pore size of 10 to 40 nm; and recovering the filtrate. The method gives rise to, e.g., a virus-safe multicomponent α-interferon composition, comprising a non-ionic detergent as a stabilizer in an amount exceeding the critical micellar concentration of the detergent and being essentially free from substances retained on a virus-filter having high virus retentive capacity.