Thisinvestigationaimstoexploredeterminantsofexposuretoparticlesize-specificweldingfume. Areasamplingofultrafineparticles(UFP)wasperformedat33worksitesinparallelwiththecol- lectionofrespirableparticles.Personalsamplingofrespirableandinhalableparticleswascarried out in the breathing zone of 241 welders. Median mass concentrations were 2.48 mg m23 for in- halable and 1.29 mgm23 forrespirable particles when excluding 26 users of poweredair-purify- ingrespirators(PAPRs).Massconcentrationswerehighestwhenflux-coredarcwelding(FCAW) with gas was applied (median of inhalable particles: 11.6 mg m23). Measurements of particles were frequently below the limit of detection (LOD), especially inside PAPRs or during tungsten inert gas welding (TIG). However, TIG generated a high number of small particles, including UFP.Weimputedmeasurements