While he was living in Arizona between 1946 and 1951, Max Ernst created at least 70 tiny gouache paintings that he called “microbes.” They range in size from a half-inch on one side to over five inches, with most between one and three inches. Many evoke fantastical landscapes while others appear completely abstract. Ernst’s interest in this series of work was sustained: he made these paintings over a period of five years, and they were exhibited regularly during his own lifetime. Today, however, the microbes are virtually unknown. Because of their relative obscurity within Ernst’s oeuvre, this essay outlines their production and early exhibition and reception, with special attention to Sept microbes vus à travers un tempérament (Seven microbes seen through a temperament). This book, comprised of life-size reproductions of 31 microbes and a poem by Ernst, positions the microbes as a distinctly surrealist, subjective interpretation of the American Southwest. The essay then contextualizes the microbes within the wider contemporary American art world and suggests that Ernst made these diminutive paintings in dialogue with the paintings of the Abstract Expressionists as those artists were rising to prominence in the wake of World War II.