 In 1863, Samuel, a prominent Hamburg merchant, sent Leonard and his brother, Julius Lewisohn, to the United States, as his firm's representatives; about three years later they were joined by their younger brother, Adolph Lewisohn, and they formed the firm of Lewisohn Brothers in January 1866.As early as 1868, the firm turned its attention to the metal trade, becoming prominent dealers in lead during that year.He married Rosalie Jacobs on June 29, 1870, in Manhattan.