We have shown that both geranylgeranyl pyrophosphate synthase and phytoene synthase from pepper and tomato chromoplasts are very similar in terms of enzymic activity and immunological properties. This enabled us to clone cDNAs specific for phytoene synthase from ripening tomato and pepper fruits and to compare their amino acid sequences with those of bacterial phytoene synthase and yeast squalene synthase. Comparison of the nucleotide sequence of the 3'-untranslated region of the pepper phytoene synthase cDNA suggests that this region was subjected to complex recombination events. RNA gel blot hybridizations revealed that induction of phytoene synthase gene expression is much stronger in tomato than in pepper fruits. In contrast with tomato, 2 phytoene synthase transcripts of different size are present in pepper leaves and fruits. Comparison of the expression pattern of the genes encoding geranylgeranyl pyrophosphate synthase, phytoene synthase and phytoene desaturase revealed that these genes are not co-regulated during pepper fruit ripening.