This paper presents a research on the impact of ISO 9000 quality management systems on manufacturing in small and medium sized enterprises (SME). In order to understand the effect of ISO 9000 implementation on firm performance, ISO 9000 certified and non-certified firms were investigated statistically to determine any significant difference between them. Then, the investigation was carried out on the effect of ISO 9000 implementation on manufacturing parameters and competitive priorities. For this purpose a sampling pool of 106 SMEs were examined of which 79 of them implemented ISO 9000 standards. Our findings show that ISO 9000 implementation makes a significant difference on firm performance between certified and non-certified firms. Similar results are also found in the analysis on manufacturing parameters and competitive priorities indicating that firms gain significant benefits. However, surprisingly no significant difference is found with respect to defective part production and manufacturing cost between the two groups. (c) 2006 Elsevier B.V. All rights reserved.