Superimposition of air, fluid, and soft tissue structures can be an important limitation of conventional vertical beam (VB) positioning in radiography, as the appearance of pneumothorax and pleural effusion can become obscured. In horizontal beam (HB) projections, the x-ray beam strikes air and fluid interfaces tangentially, making them more evident. This study evaluated HB radiography for diagnosis of pneumothorax and pleural effusion in dogs (n = 42) and cats (n = 5) with known history of thoracic trauma or with signs of pleural space disease. Thoracic radiographs were obtained using conventional VB right lateral (RL), left lateral (LL), and ventrodorsal (VD) or dorsoventral views, with at least 1 additional VD HB projection obtained in either RL or LL recumbency. Statistical analysis showed pneumothorax was significantly more likely to be detected and/or given a higher grade of severity in the RL HB projection as compared with other views. Radiologists reported more confidence in diagnosis when using VB views. When added to conventional VB projections, HB radiography can raise confidence in determining the presence and severity of pneumothorax and pleural effusion in dogs and cats. Commentary The authors should be praised for researching techniques to make the diagnosis of pneumothorax and pleural effusion with higher confidence; however, a gold standard (eg, CT) for comparison was not provided, so the findings can be somewhat subjective. In most clinics, the digital detector is permanently mounted in the Bucky tray; therefore, the HB technique cannot be performed by placing it above the table. A discussion of ultrasonographic detection of pneumothorax and pleural effusion would have been beneficial, as it has potential to be cage-side, which is safer due to lack of radiation with minimal patient manipulation and can be used to guide aspiration when indicated.—Jean K. Reichle, DVM, MS, DACVR Source Detection of pneumothorax and pleural effusion with horizontal beam radiography. Lynch KC, Oliveira CR, Matheson JS, et al. VET RADIOL ULTRASOUND 53:38-43,