We studied the presence of apolipoprotein B (apo B) by immunoelectrophoresis in subretinal fluid (SRF) and serum from 15 rhegmatogenous retinal detachments and 5 retinal detachments with proliferative vitreoretinopathy (PVR). Apo B concentration +/- standard deviation was 1.49 +/- 1.06 mg/dl in SRF and 108.41 +/- 40.22 mg/dl in serum. Only in four cases was apo B not detected in SRF. We found no significant correlation between apo B concentrations in SRF and apo B levels in serum. We did not find a positive correlation between apo B concentrations in SRF and the duration and size of the detachments. There was no statistical relationship between the presence of PVR and apo B levels. This phenomenon suggests the preservation of the outer blood retinal barrier during rhegmatogenous retinal detachment.