Flowering of the long day plant Hyoscyamus niger L., which is strictly photoperiodically controlled, was induced by 58 h continuous white light. The RNA from the leaves was isolated from photoperiodically induced and non‐induced plants and the poly(A)‐rich RNA separated by affinity chromatography on oligo‐dT‐cellulose. The poly(A)‐rich RNA was translated in vitro in the presence of 35S‐methionine using a rabbit reticulocyte lysate. Subsequent separation of the translation products by two‐dimensional polyacrylamide gel electrophoresis and fluorography allowed a comparison of the polypeptide pattern from induced and non‐induced leaf m‐RNA. The results indicate that induction of flowering is reflected by changes in the translation of several leaf polypeptides. These polypeptides were characterized by their isoelectric points and molecular masses.