With the introduction of performance factor, K, in IS:1893-1984, a R.C. frame building may be detailed as ordinary concrete frame (with K = 1.6) as per IS:456-1978 or as ductile concrete frame (with K = 1.0) as per IS:4326-1976. Three real-life multistorey R.C. frame buildings have been designed for seismic zones I, III and V. The frames have been detailed as ordinary frames with K = 1.0 and 1.6 and as ductile frames. Quantity of reinforcement steel and the cost implications for different zones and detailing criteria have been compared. It is seen that with the introduction of K, cost of construction has gone up especially in zones II and III. In zones lil to V it is more economical to provide ductile frame than the ordinary frame.