This protocol details a culture technique for neonatal mouse retina that allows the assessment and quantification of acute responses of developing blood vessels to pharmacological manipulation. The technique has proven to be a useful tool for elucidating the molecular mechanisms that underlie the guidance of tip cells in the complex scenario of the angiogenic sprouting process. This culture setting allows the acute stimulation or inhibition of cellular functions of endothelial cells in their physiological environment ex vivo. Compared with other existing techniques, such as retinal injections in animals, the explant culture described here is an easily manageable and highly flexible alternative that allows pharmacological manipulations of the developing retina vessels. The technique involves swift extraction of retina from intact eye and retinal flat mounting on a hydrophilic membrane with minimum disturbance of the tissue. The responses of tip endothelial cell sprouting activity and filopodial extension to different angiogenic and angioinhibitory factors can be evaluated within only 4 h. The whole process for the retinal explant cultures and stimulation can be completed in 10 h.