Gaseous and particulate matter emissions from two California high-rise layer houses were continuously measured and monitored for two years from October 2007 to October 2009. Each house had 34,000 laying hens in cages. The monitoring site was set up in compliance with a US EPA-approved site monitoring plan, standard operating procedures, and quality assurance project plan. The results showed the daily mean emission rates of ammonia, hydrogen sulfide and carbon dioxide were 0.97 g/hd-d, 1.28 mg/hd-d and 91.4 g/hd-d, respectively. The daily mean emission rates of PM2.5 PM10 and total suspended particles (TSP) were 5.9, 33.3, and 78.0 mg/hd-d, respectively. The influence of environmental conditions, ventilation rate, manure management practices on various emissions rates are presented.