Human lung fibroblasts (HLF) were labeled with 35SO2-4 for 48 h and extracted with a guanidinium chloride buffer. A fraction of the extracted heparan sulfate proteoglycan (HSPG) appeared micelle-associated. In the absence of detergent these HSPG eluted in the void volume of Sepharose CL2B columns. In the presence of detergent these HSPG were included in Sepharose CL2B (Kav = 0.55) and 4B (Kav = 0.3) columns. This type of HSPG was specifically associated with isolated HLF cell membranes, suggesting that it may represent a fraction of integral membrane proteoglycans. Most of the HSPG in the HLF monolayers, however, eluted in the included volume of Sepharose CL2B (Kav = 0.4) and CL4B (Kav = 0.1) columns in the absence of detergent. This type of HSPG was not affected by detergent and was specifically retained in 'extracellular matrix' preparations. The medium of HLF monolayers contained HSPG of similar Mr as the membrane-associated HSPG. Of these three distinct HSPG fractions only the membrane-associated form could be incorporated in liposomes, confirming that the HSPG in this fraction may be integral membrane components.