Aqueous humor lactate dehydrogenase (LDH) levels were assayed for 23 patients with histologically proved retinoblastoma. The mean aqueous level was 1,886 IU/liter. Twenty-one of these patients had an aqueous humor LDH level above the normal mean. Clinicopathological parameters were determined and evaluated using standard statistical formulas. Only the presence of tumor in the anterior chamber correlated significantly with the aqueous humor LDH level. The following clinical features did not correlate with aqueous humor LDH levels: sex, family history, bilaterality, prior treatment, presentation age, enucleation age, and metastasis. The following pathological features did not correlate with aqueous humor LDH levels: calcification, necrosis, rosettes, inflammation, choroidal or optic nerve invasion, or neovascularization.