Antibodies directed against purified Ca‐ATPase from sarcoplasmic reticulum, calsequestrin and parvalbumin from rabbit fast‐twitch muscle were raised in sheep. The specificity of the antibodies was shown by immunoblot analysis and by enzyme‐linked immunoadsorbent assays (ELISAs). IgG against the sarcoplasmic reticulum Ca‐ATPase inhibited the catalytic activities of Ca‐ATPase from fast‐twitch (psoas, tibialis anterior) and slow‐twitch (soleus) muscles to the same degree. In non‐equilibrium competitive ELISAs the anti(Ca‐ATPase) IgG displayed a slightly higher affinity for the Ca‐ATPase from fast‐twitch muscle than for that from slow‐twitch muscle. This suggests a fiber‐type‐specific polymorphism of the sarcoplasmic reticulum Ca‐ATPase. Quantification of Ca‐ATPase, calsequestrin and parvalbumin in various rabbit skeletal muscles of histochemically determined fiber composition was achieved by sandwich ELISA. Ca‐ATPase was found to be 6–7 times higher in fast than in slow‐twitch muscles. A slightly higher concentration was found in fast‐twitch muscles with a higher percentage of IIb fibers when compared with fast‐twitch muscles with a higher percentage of IIa fibers. Thus Ca‐ATPase is distributed as follows, IIb ≥ IIa ≫ I. Calsequestrin was uniformly distributed in fast‐twitch muscles independently of their IIa/IIb fiber ratio and displayed 50% lower concentrations in slow than in fast‐twitch muscles (IIb=IIa > I). Parvalbumin contents were 200–300‐fold higher in fast than in slow‐twitch muscles. Significantly lower parvalbumin concentrations were found in fast‐twitch muscles with a higher percentage of IIa fibers than in fast‐twitch muscles with a higher percentage of IIb fibers (IIb > IIa ≫ I).