The alkaloids of Uncaria tomentosa micropropagated plantlets and root cultures were isolated and identified by NMR and mass spectrometry. Plantlets yielded pteropodine (1), isopteropodine (2), mitraphylline (3), isomitraphylline (4), uncarine F (5), speciophylline (6), rhynchophylline (7) and isorhynchophylline (8). In plantlets growing under continuous light, tetracyclic alkaloids 7 and 8 decreased from 20 +/- A 1.8 at 2 months to 2.2 +/- A 0.33 mg/g dry wt at 6 months, while the pentacyclic alkaloids 1-4 increased from 7.7 +/- A 1.4 to 15 +/- A 0.05 mg/g dry wt, supporting their biogenetic conversion. Micropropagated plantlets produced four times more alkaloids (27.6 +/- A 3.1 mg/g dry wt) than greenhouse plants. Plantlet roots yielded 3, 4, 8 and the glucoindole alkaloids 3 alpha-dihydrocadambine (9) and dolichantoside (10), the last one not previously found in Uncaria.