4-hydroxy-3-methoxymandelic acid (HMMA) excretion in retinoblastoma

4-Hydroxy-3-methoxymandelic acid (HMMA) concentrations in aqueous humour, urine, and serum were simultaneously estimated to determine if these levels were raised in cases of retinoblastoma. The catecholamine content of aqueous humour was significantly higher than that of urine and serum, but as there was no significant difference in the HMMA concentration in retinoblastoma and other non-malignant conditions it seems likely that retinoblastoma is not a catecholamine-secreting tumour.