In this paper, I would like to explore the place and role of collectors at the 4th "Impressionist" exhibition in 1879. This exhibition is indeed an intriguing case study, since nearly 37% of the works belonged to various owners, and it differs from the eight other "impressionist" exhibitions in the high number of works on loan and mentioned as such in the catalogue. Among the forty or so lenders identified, we find well-known personalities such as Georges de Bellio, Théodore Duret, Ernest May or Eugène Murer, as well as artist-collectors such as Gustave Caillebotte, Paul Gauguin and Henri Rouart. Among the artists, Edgar Degas, Jean-Louis Forain, Claude Monet and Camille Pissarro were the ones who mostly called on collectors and, in their cases, a large part of their works were not for sale. In this communication, I would like to explain the alliance of these artists with a heterogeneous group of collectors who have enabled them to exist on the art scene and to create a new market. Very little mentioned in the press, these collectors appeared only on a discreet mode. But the questions about them remain numerous: did they have any links with each other? How was their support at the 1879 exhibition crucial? Did their participation in the exhibition as lenders stimulate their desire to buy and direct them towards artists they had not previously collected? By precisely analysing their careers, as well as the specificity of the 4th painting exhibition, I will try to answer these questions, which help to revalue the role of collectors and the public at the end of the 1870s. From then on, I will approach them not from a monographic and diachronic angle, but in a synchronic and systemic way, since I will study a given moment, that of the 4th painting exhibition which took place between April 10 and May 10, 1879, and an ecosystem, understood here as a community of artists and collectors linked by a project and acting in an interdependent way.