Amyloid P component (AP) is a matrix glycoprotein of adult renal glomeruli. To establish whether the deposition of AP in glomeruli is an age-related phenomenon, this study used indirect immunofluorescence (IF) to investigate 34 renal biopsy specimens and 11 renal autopsy specimens. The biopsy specimens were taken from 9 patients (age range from 2 to 38 years) with normal glomerular morphology and from 25 patients (age range from 4 to 56 years) with various renal diseases. All autopsy specimens (age range form 2 months to 28 years) showed normal glomerular morphology. AP was not detected in glomeruli before age 6. By age 14, the IF intensity reached the level of the adult specimens, in which a strong fluorescence was seen along the basement membranes and within the mesangial matrix. In renal diseases, glomerular AP also appeared after age 6, although varying in its location and intensity. In conclusion, our results indicate that the appearance of AP in glomeruli is an age-related phenomenon, the pattern of which varies in renal diseases.