Two genetically distinct types of collagen, Type SQ-I and SO-II, were isolated from the mantle muscle of the squid Todarodes pacificus, and their respective components, alpha 1(SQ-I) and alpha 1(SQ-II), were resolved from the two types of collagen by column chromatography. Rabbit antisera against these collagens and or components were prepared and their immunological properties were examined by immunoblot analysis. The anti-Type SQ-I collagen serum reacted intensely to the alpha 2(SQ-I) and alpha 2(SQ-II) components but faintly to the alpha 1(SQ-I) and alpha 1(SQ-II) components. The anti-Type SO-II collagen serum reacted intensely to the alpha 1(SQ-II) component but showed little reactivity to the other alpha components. Although the anti-alpha 1(SQ-I) component serum was rather crossreactive for the alpha 1(SQ-II) component, it showed a high specificity to the alpha 1(SQ-I) component by treatment with 20 or 50 mu g of Type SQ-II collagen/1 mu l of serum at 37 degrees C for 48 h. On the contrary, the anti-alpha 1(SQ-II) component serum displayed a high specificity to the homologous antigen. These results suggest that the anti-alpha 1(SQ-I) and anti-alpha 1(SQ-II) component sera can be applied to immunohistochemical experiments as antibodies which recognize Type SO-I and SO-II collagens, respectively. The distribution of these two molecular species of collagen in the mantle skin and arm muscle was also examined by immunoblot analysis. Type SQ-I and SO-II collagen fractions from the mantle skin and arm muscle reacted to these four antisera in the same way as those prepared from the mantle muscle. These results demonstrate the wide distribution of these two types of collagen not only in the mantle muscle but also in the mantle skin and arm muscle.