The institution implementing the state's social policy in the first half of the 1930s became the Social Insurance Institution, established after the amalgamation of the insurance system. By the end of the 1930s, the Polish ZUS was one of the fastest growing insurance institutions in Europe. The funds from the financial surpluses created by the reinvestment of insurance premiums were used by ZUS for construction (hospitals, sanatoriums, residential buildings) and pro-health activities. The mighty modernist ZUS buildings were constructed in Poznań (1931) and Gdynia (1936).

In Lviv, on Zielona Street, a building was constructed for ZUS that is one of the best examples of modernism. The building was designed by Jan Bagieński (1883-1967), who at the time was at the peak of his career as both a practising architect and academic lecturer, as a professor at the Lviv Polytechnic. The bulk of Bagienski's architectural legacy is stylistically neoclassical. He even developed his own method of transforming the proportions of classical orders to adapt them to modern building standards and technological possibilities. In designing the complex massing of the ZUS, despite its functionalist guidelines, he remains a profound apologist for classical architecture. The vertical bands of windows or the semi-circular bay window, which emphasise the verticality of the edifice topped by a prominent cornice, are testimony to the tum. The main entrance with a vestibule and a representative staircase glazed over the entire height of the building define the axis of the main façade. The construction of the building lasted from 1937 to 1939 and became the architect's most recognisable work. However, the building did not manage to fulfil its original function.

During the Nazi occupation, the modern premises were adapted as a research institute under the name: Institute for Typhoid and Virus Research. The purpose of the institute was to produce a vaccine for the German occupiers. It was led by Lviv University professor Rudolf Weigl. He created a widely renowned spotted fever research centre in Lviv, a meeting place for the most eminent people of science even between the wars. Even then, the world-famous biologist had already discovered a vaccine for this one of the most deadly diseases in history.

During the war, the Weigl Institute on Zielona Street became a place where the lives of Lviv residents were saved by employing them to feed the lice used in the research. The Institute's collaborators, including the so-called lice feeders, received protective papers and a food deputation. In this way, the professor helped around four thousand people. He saved, among others, Stefan Banach and Zbigniew Herbert. The typhoid vaccine produced at his Institute was illegally distributed to civilians fighting in the underground, and was also sent to the Lviv and Warsaw ghettos.

A great biologist and a man who saved thousands of lives, although he was nominated for the Nobel Prize three times, he never received it. He was buried in Rakowicki Cemetery in Krakow.

Today, the building houses the Lviv sanepid and the Department of Microbiology of the Medical University.