This paper presents a case study performed in an industrial project where we introduced and evaluated a method for supporting contract-based program development. The project constructed a large software system and involved around 30 people for 8 months. This paper reports on the designers' and programmers' attitudes towards programming by contract and how they perceived the effect the method had on their work. The results show that the designers and programmers were generally positive to contract-based program development and believed that the quality of their products would improve as an effect of the method