Ganglioside-and glycoprotein-bound sialic acid in endplate and non-endplate regions of rat diaphragm muscles were assessed 1-16 days after phrenic nerve transection. Sialic acid in glycoproteins (90% of total) and gangliosides (10% of total) from intact hemidiaphragms was distributed uniformly throughout endplate and nonendplate regions. Afer denervation, the total sialic acid per hemidiaphragm increased (days 1-4) and reached a maximum level (days 8-12) which remained constant (days 12-16). These sialic acid changes reflected increments in gangliosides (40% over control), which occurred simultaneously in endplate and non-endplate regions (days 1-8), and increments in sialoglycoproteins (70%-80% over control), which took place much earlier in endplate (days 1-8) than in nonendplate (days 8-14) regions. The results of this study, together with previous data, favor the hypothesis that maintenance of both sialoglycoproteins and gangliosides depends upon an intact innervation, probably through separate mechanisms involving different neurogenic factors.