Lack of effective competition in factor markets often produces allocative or price inefficiencies in the manufacturing sector of developing countries like Pakistan. Such inefficiencies are common due to distortion in factor markets leading to the use of inappropriate factor proportions Lau and Yotopoulos (1971, 1972), Yotopoulos and Lau (1973), Burki, et al. (1997), Khan (1998), Ahmed (1999), Zafar (2000). Pakistan is also one of the country where labour is abundant but capital and raw material are scarce. Our finding undermine estimates of elasticities of demand and substitution based on classical assumption that factor markets are perfectly competitive i.e. Kazi, et al. (1976), Kemal (1981), Battese and Malik (1987, 1988, 1993), Malik, et al. (1989), Mahmood (1989, 1992), Zahid, et al. (1992) and Khan and Rafiq (1993). In order to discuss the cost structure of the manufacturing sector we will estimate well behaved translog cost function.