Completely polymerizing olefinic monomer feed, in contact with a coordination catalyst suitable for olefin polymerization, in a mold having the shape of the article, at conditions under which the polymer is produced as a coherent, useful article in the shape of the interior of the mold, and removing the article from the mold. This method permits the production of polyolefin articles which are difficult or impossible to produce from polyolefin powder or pellets by conventional methods, such as articles of polyolefins of such high molecular weight that the polymer would not be processable by a melt process; articles containing extremely high filler loading; articles containing interconnected reinforcement; and articles from molds which require substantial flows through narrow passages.