Extensive tracer experiments were carried out on Tulipa with the aim of determining the structure and biosynthesis of sporopollenin. The radiolabeled precursors were applied using an improved technique previously selected. The sporopollenin fraction was purified using either a gentle method — hydrolyzing enzymes (pronase, amylase, amyloglucosidase, cellulase, pectinase and lipase) and alkaline hydrolysis (method A) — or by a conventional aggressive procedure, where the material was enriched by alkaline hydrolysis and treated several days with 80% phosphoric acid (method B). The 14C-labeled precursors applied were mevalonate, glucose, acetate, malonic acid, phenylalanine, tyrosine, p-coumaric acid. Regardless of the method of enrichment, a higher level of incorporation into the sporopollenin fraction was always seen with [U-14C]-phenylalanine. The level of radioactivity found in sporopollenin labeled by phenylalanine or malonate was sufficiently high for the labeled polymer to be degraded and the products released analyzed for the first time. In the case of phenylalanine-labeled sporopollenin, the main degradation component, p-hydroxybenzoic acid, was also the most heavily labeled substance. This result was not dependent on the procedure used for sporopollenin enrichment. These findings are interpreted as meaning that phenylpropane metabolism via phenylalanine-ammonia lyase is involved in sporopollenin biosynthesis.