The internal structure of agarose gels has been monitored by measuring their intrinsic birefringence. The sign and amplitude of the intrinsic birefringence vary from one gel to another and at different locations within each gel, suggesting that the internal structure of the agarose matrix is macroscopically variable. The sign and amplitude of the electric birefringence, measured separately, also vary from one gel to another and at different locations within each gel. The average absolute amplitudes of the intrinsic birefringence and the electric birefringence increase linearly with agarose concentration, as expected. However, there is no correlation between the signs and amplitudes of the intrinsic and electric birefringence, suggesting that the electric field orients subdomains within the larger, intrinsically birefringent regions of the gel matrix.