A rapid and cost-effective combination tapered fiber-optic biosensor (CTFOB) dip-probe was used for quantitative estimation of interleukin (IL)-6 in serum/plasma samples. Sandwich immunoassay was used as the detection technique. Probes could successfully detect presence of IL-6 in two serum samples, non-neoplastic autoimmune patient (lupus) sample and lymphoma patient sample. The estimated amount of IL-6 in lupus patient sample was 4.8 ± 0.9 pM and in lymphoma patient sample was 2 ± 1 pM. It is demonstrated that the developed CTFOB dip-probe is capable of quantitative estimation of proteins in serum/plasma samples with high specificity. © 2010 Copyright SPIE - The International Society for Optical Engineering.