Objectives: The study investigated the concentrations of metals (chromium [Cr], manganese [Mn], cobalt [Co], nickel [Ni]) in the blood plasma and urine of Polish welders exposed to these elements contained in welding dust/fumes based on the results of biological monitoring, analyze the interrelationships between these elements, and attempt to correlate these data with telomere length. It is believed that telomere length can be considered a marker of exposure, including occupational. Analysis of questionnaire surveys was also taken into consideration. Material and methods: The study included 118 male welders and 51 age-matched male controls. Metals analysis in plasma and urine were determined by ICP-MS technique. Telomere length was measured in blood genomic DNA using the qRT-PCR method. Results: Welders had significantly higher plasma levels of Cr, Ni, and Mn (p < 0.0001, respectively). Total concentrations of Cr, Ni, and Mn in the urine of pre-shift subjects were significantly higher compared to controls. Cobalt concentration in urine of exposed welders was significantly higher (p < 0.02) than in control group. Telomere length was exactly the same in the welder group compared to the control (mean ± standard deviation 0.99±0.41 vs. 0.99±0.52, respectively). Plasma and urine metal concentrations and telomere length were also studied in groups of welders in relation to personal protection equipment. Differences were found in plasma and urine metal concentrations according to the aspirators used. Statistically significant linear correlations were found between plasma and urine concentrations of the determined elements both before and after the work shift. Conclusions: The findings suggest a positive relationship between Ni and Mn (end-shift) concentrations and telomere length, the effect which remained statistically significant even after adjusting for age and metabolic status. This indicates a complex interplay between metal exposure and biological aging markers. However, the relationship between exposure to welding fumes and changes in telomere length in welders requires further in-depth research. Int J Occup Med Environ Health. 2025;38(1)