To examine the sources of IgG in nasal secretions, nasal provocation tests with histamine (H) and methacholine (MC) were performed on 22 subjects. Nasal lavages were assayed for IgG, total protein, albumin (Alb), nonsecretory IgA (nonsIgA), and secretory IgA (sIgA). H stimulation dramatically increased the secretion of IgG, nonsIgA, and Alb and also increased the proportion of these proteins compared to total protein. H-induced protein secretion was significantly inhibited by nasal pretreatment with chlorpheniramine maleate but was unaffected by atropine sulfate. sIgA was also stimulated by H challenge, but unlike IgG and other vascular proteins, the proportion of sIgA to total protein (sIgA percent) decreased after H challenges. MC stimulation also increased secretion of IgG, Alb, nonsIgA, and sIgA but did not alter their proportions, compared to total protein. Topical atropine significantly inhibited secretion of all proteins, suggesting a mode of transportation mediated by glandular muscarinic receptor stimulation. Thus, MC can increase the amount of IgG secretion, whereas H increases both the amount and relative proportion of IgG in nasal secretions. These data suggest that pharmacologic stimulation of IgG into nasal secretions may be used as a total to modulate mucosal immunity.