A total of 44 eyes of 22 ferrets were examined by B-mode ultrasonography. Four dimensions were measured: the distance from the corneal surface to the anterior lens surface (M1), the axial lens thickness (M2), the distance from the posterior lens surface to the retina (M3) and the distance from the anterior cornea to the retina (M4). The values obtained were (mean, standard deviation, range): M1: 1.31 +/- 0.16 mm (1-1.7); M2: 3.42 +/- 0.15 mm (3.2-3.7); M3: 2.26 +/- 0.11 mm (2.1-2.5); M4: 7 +/- 0.24 mm (6.4-7.7). To our knowledge this is the first description of ocular biometric measurement in the ferret. These values show little variability of ocular dimensions in ferrets.