Abstract The purpose of the present study was to compare the procalcitonin (PCT), neopterin, interleukin-8 (IL-8), interleukin-10 (IL-10) and interleukin-12 (IL-12) levels with those of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) in cancer patients with (56) and without infection (36) and to evaluate their ability to differentiate infections from neoplastic fever (n = 10). The infection group had statistically higher levels of CRP (91 vs. 19 mg/l, p < 0.001), PCT (0.28 vs.0.12 ng/ml, p < 0.001), neopterin (12.8 pg/mL vs. 4.0 pg/mL, p < 0.001), IL-8 (27.7 vs. 16.9 pg/ml, p = 0.032), IL-10 (3.8 pg/mL vs. 1.8 pg/mL, p = 0.005) and ratios of neopterin to IL-12 (1.74 vs. 0.11, p < 0.001), and IL-10 to IL-12 (0.4 vs. 0.05, p < 0.001) than the non-infection group. After a subdivision of the study population into patients with local or advanced disease, the differences between the study groups remained statistically significant for CRP and neopterin both in local (p < 0.05 and p < 0.001) and advanced diasease (p < 0.01 and p < 0.001) and in advanced disease for PCT (p < 0.001), IL-10 (p < 0.05), IL-12 (p < 0.05), neopterin to IL-12 ratio (p < 0.01) and IL-10 to IL-12 ratio (p < 0.01). The ESR levels did not differ between the study group (50 vs. 42 p = 0.16), while the IL-12 values were lower in the infection group (10.6 pg/mL vs. 71.6 pg/mL, p = 0.007). The tumor load did not influence any of the studied infection markers within the study groups. For identifying bacteremia by area under the operating characteristics curves (AUC), the highest values were obtained for PCT (0.92) and neopterin (0.90), and slightly lower values were recorded for the ratios neopterin to IL-12 (0.79) and IL-10 to IL-12 (0.75). None of the markers or ratios were good for differentiating non-bacteremic infections from neoplastic fever, the AUC values rangin from 0.27 for ESR to 0.61 for IL-10 to IL-12 ratio. The simultaneous use of the ratio of neopterin to IL-12 with its high sensitivity (82%) and that of IL-10 to IL-12 with its high specificity (90%) should be further studied.