Prompted by our impression that microtubuloreticular complexes (MTRC) are frequently observed during electron microscopy at the Red Cross War Memorial Children's Hospital, Cape Town, we reviewed all specimens submitted for routine ultrastructural examination during a 1-year period. Our impression was confirmed. MTRC were present in a high proportion of cases, especially in vascular endothelium of renal biopsies. As all 9 cases of hepatitis B-associated membranous glomerulonephritis were positive for MTRC, we also reviewed the previous 20 cases with this diagnosis and these were also all positive. Hepatitis B-associated membranous glomerulonephritis is common in our region. MTRC are probably induced by a supposedly uncommon heat labile alpha-interferon. Elevated serum levels of this interferon are known to occur in systemic lupus erythematosus and acquired immunodeficiency syndrome. We propose that children with intercurrent infection in our region frequently respond with alpha-interferon, promoting MTRC formation.