Career
He is best known for his work on ultraproducts, in particular for "Łoś"s theorem", which states that any first-order formula is true in an ultraproduct if and only if it is true in "most" factors (see ultraproduct for details). He was faculty at academies in Wrocław, Toruń, and Warsaw. In 1996 Łoś suffered from a severe brain stroke.
He was thenceforward ill until his death in 1998.