The amylase isoenzymes activities in serum and urine from 75 children treated for complications of mumps were evaluated. The clinical observations, especially in cases with suspected pancreatitis, were compared with the P- and S-type amylase activities. Increased total activity of serum amylase in 79% of patients was due to increased S-type amylase. However, in 39% of patients there was also a markedly increased P-type serum amylase. Amylase isoenzymes may offer a new insights into the relationship between the pancreas and the parotid glands in mumps.