Fifty-seven children in a fairly new day-care institution were examined daily by impedance audiometry through 4 weeks. A Madsen Electronics ZS 330 tympanoscope was used. The tympanometric curves were divided into types A, C1, C2, and B, indicating pressures over -99 mmH2O, from -100 to -199 mmH2O, below -199 mmH2O and completely flat curves, but in cases in which the compliance was less than 0.25 ml, combined with an absent ipsilateral stapedial reflex, were also interpreted as type B. The object was to ascertain how quickly the types changed and how stable the B curves were. Types A + C1, C2, and B changed daily into other types in 4.3%, 32.8%, and 9.5% respectively. A total of 43 episodes of B curves occurred. Of them 16 lasted for only one day and thereamongst 9 became quite flat. Only a few lasted for 8-23 days and 8 for 26 days or over.