The aim was to determine the effect of respiratory illness and season on carriage rates in the upper airways of Streptococcus pneumoniae, Hemophilus influenzae and Moraxella catarrhalis in normal children. Sixteen healthy children, 1-10 years old, amenable to weekly sampling were followed longitudinally for at least three seasons of the year. Respiratory symptoms were recorded daily; weekly nasal aspirate/wash samples were cultured on selective agars. Urea concentration in samples was used to define dilution of secretion. 68% of 950 samples were culture positive; 44% of positives had two or all three species. Each species was detected in about one third of samples. Bacteria were detected in 76% of samples during illness vs. 65% during wellness (p=0.004). Seasonal carriage rates varied from 56% in summer and fall to 85% in winter. There was a strong inverse correlation between dilution of secretion and bacterial detection rate in illness and wellness aspirate samples during the four seasons (r=-0.82, p=0.01). Detection of bacteria varied with the amount of secretion in the sample. This variation accounts for the apparent differences in bacterial carriage during illness vs. wellness and during different seasons.