Four commercial high-rise layer houses were monitored for a year to determine manure production and nutrient concentration characteristics. Each house contained 80,400 to 124,500 mature Hy-Line W-36 birds. The solid manure collected as it accumulated beneath the cages for a year prior to being hauled out. The objective of the research was to accurately characterize the manure production to facilitate better nutrient planning. Manure volume and bulk density were measured and samples were collected monthly and analyzed for moisture, Kjeldahl nitrogen, ammonia, phosphorus, potassium, calcium, and other chemical constituents. The measured manure production averaged 5.6 Mg (or 6.2 ton)·(1000 birds) –1 (year –1 on a dry basis. On a wet (as-is) basis the measured production was 9.52 Mg (or 10.5 ton)·(1000 birds) –1 (year –1 at 41% moisture. The measured manure N-P 2 O 5 -K 2 O contents were 18.5-41.0- 26.0 kg/Mg (37-82-52 lb/ton) on an “as-is” basis or 30.8-69.0-44.0 kg/Mg (62-138-88 lb/ton) on a dry basis. When manure production and nutrient concentrations were combined, measured nitrogen production was 52.8% less, phosphorus was 29.5% greater, and potassium was 27.8% greater, than the respective current Iowa estimates. The average calcium concentration for all four sites studied for the year was 10.0% (as-is basis). The manure handling system had a significant impact on manure characteristics. Scraper systems had a lower moisture content and a lower percentage of the nitrogen in ammonia form (29.8% moisture, NH 3 = 20% of TKN) than systems that dropped the manure into storage immediately (46.9% moisture, NH 3 = 30% TKN).