We have proved highly significant differences in glucose concentration and activity of alpha-amylase in haemolymph of two growth classes of Planorbarius corneus with width of shell smaller and equal or greater than 20 mm, respectively. Both these parameters were higher and were characterized by greater range of individual variability in snails with smaller width of shell. Any differences in levels of total protein and haemoglobin in haemolymph of these animals, in comparison with adult individuals, were not observed. Effect of infection of the pulmonary cavity of investigated snails with Chaetogaster limnaei limnaei on the examined parameters was not ascertained.