Tracer experiments were carried out with anthers ofTulipacv. Apeldoorn andCucurbita maxima. Labelled sporopollenin fractions were enriched either by a conventional harsh or by a gentle method. In each case phenylalanine was incorporated at higher rates into the sporopollenin fraction ofTulipathan any of the other precursors used. The high incorporation of phenylalanine was observed at several stages of the postmeiotic development ofTulipaanthers. Even higher incorporation rates were obtained usingCucurbitaanthers. The incorporation of [U-l4C]-phenylalanine, [ring U-14C]-phenylalanine and [l-14C]-phenylaIanine into the sporopollenin ofTulipawas compared. The results indicate, that the whole carbon skeleton of phenylalanine is incorporated, pointing to an involvement of the phenylpropanoid metabolism. After potash fusion of a sporopollenin fraction labelled via [ring U-14C]-phenylalanine, p-hydroxybenzoic acid was the main labelled product among the ether soluble acids.