The extensional flow properties of a lyotropic colloidal suspension of sepiolite clay have been explored by combined dichroism and small-angle light scattering measurements. The clay particles are rigid rods 1 micrometer long and 0.010 micrometer in diameter. Analysis of extensional transient regimes of the flow reversal type revealed the main characteristics of the extensional flow of these suspensions. Extensional flow was applied to a thin film of sepiolite suspension in an extension cell of the four-roll mill type. Near a critical volume fraction, the behavior of the colloidal suspension changes from that of an isotropic system to that of a nematic system. In the isotropic behavior domain, flow reversal leaves no permanent orientation in the sample during the relaxation phase. In the nematic behavior domain, permanent orientations of the structure were observed. When extension is interrupted in this phase, the system relaxes but an orientation persists following the last direction of extension. As extension rate increases, the structure becomes more oriented. In the nematic phase, a critical strain rate separates two flow regimes. First, there is a stable, so-called strong flow rate, which occurs above , where flow reversal flips the orientation of the structure in each direction of stretching. Second, an unstable flow regime referred to as weak flow occurs below , where flow reversal is not sufficiently strong to flip the orientation of the structure imposed by the preceding stretching. These experimental observations agree with the theoretical predictions of the model proposed by Maffetone et al. [1]. What is new in the present case is that the colloidal suspension is of 3-dimensional type, whereas previous experimental validations of the model concerned only 2-dimensional crystalline liquids [1-3].