No farm-based research information is presently available about the agronomic performance of certified organic cotton production systems in California. Certified organic production could provide a profitable production alternative, reducing energy costs and environmental impacts, and increasing farm income. The goal of this study was to monitor and compare variables influencing crop productivity and production efficiency in both conventional and transitional/certified organic cotton production systems in the northern San Joaquin Valley, California. Replicated mapping and picking of sample plants at harvest in organic and conventional production systems from 1992-1994 showed that yields did not differ in the two systems, however number of open bolls, first position retention, and yield per plant were higher in the organic production system due to lower plant density. Average internode length, an index of plant vigor, did not differ significantly between production systems. Introduction