Tryptophan (TP), 5-hydroxytryptophan (5-HTP), 3-indoleacetic acid (IAA) and serotonin (5-HT) were separated by TLC, with chloroform-methanol-ammonia (12-7-1) (v-v-v) as eluent and cellulose as stationary phase. A fibre optic-based fluorescence instrument for in situ scanning was used for quantitative measurements. The compounds were determined over the range 10–100 ng, with relative standard deviations between 1.70–6.52% and detection limits over the range 16.39–22.50 ng.