Experiments have been performed on various types of living materials (small vertebrates and invertebrates, bacterial cultures, germinating seeds) with a new Calvet microcalorimeter installed at the University of Montreal, thanks to a grant from the National Research Council. In this article, curves of thermogenesis (thermograms) of some species of Melanoplus (Orthopterae) are first examined; they vary according to individuals, species, sex, age, stage of development, temperature of the ambiance, etc. Under respiratory conditions permitting a long survival (many days), several types of normal thermogenesis can be distinguished among them. When insects are placed in closed cells, some hours later their thermograms become strongly modified; a strong paroxysm of thermogenesis occurs when the animal undergoes the first effects of asphyxia and lasts, with jerks, during two or three hours; then follows a comatous depression leading to death. Those troubles seem imputable here to accumulation of carbon dioxide, not to lack of oxygen in the calorimetric cell. In other experiments, performed in the presence of small quantities of sodium hydroxide in order to absorb the carbon dioxide elaborated, the insects remain alive for several days, with their thermograms reaching a constant, thinly undulated regimen. We have also investigated the thermogenesis of many other species of insects among Orthopterae, Dictyopterae, Lepidopterae, Dipterae, and Coleopterae. Besides specific differences their thermograms display strong variations at times of molting, metamorphosis, laying of eggs, etc. Microcalorimetry is thus likely to offer interesting applications for analyzing stages of development as well as physiological responses to environmental factors.