Hydroxymethylfurfural and furfural can be estimated automatically at 60 samples/h in a continuous-flow system. The hydrazone of the furfural with 5-hydroxybenzoylhydrazine is formed in aqueous solution and dialyzed into methanol or other lower alcohols on the recipient side of the dialyzer. The fluorescence of the zinc chelate of the hydrazone is measured. The procedure has applications for estimating the extent of hemoglobin glycosylation and for measuring the levels of hydroxymethylfurfural in some beverages. For more exacting work it can be used in conjunction with corrections from a blank channel or after preliminary specimen purification. Its specificity, though limited, compares favorably with other methods, while having advantages in sensitivity and capacity for high-throughput batch processing.