Heptanal (CAS No. 111-71-7) was evaluated for acute inhalation toxicity. The test substance was administered to Sprague-Dawley CD rats (3/sex) at an average analytical concentration of 4.7 mg/l for 4-hours. All animals survived the duration of the study. Observations noted during exposure included labored breathing, gasping, salivation, and decreased activity. Clinical signs noted during the first day included a few secretory responses and yellow ano-genital staining. During the week after exposure, all animals gained weight and exhibited a few scattered responses such as dry rales and nasal discharge.