Recent advances in mass spectrometry and in vivo isotopic labeling have enabled proteome-wide analyses of protein turnover in complex organisms. Here, we describe a protocol for analyzing protein turnover rates in mouse tissues by comprehensive (15)N labeling. The procedure involves the complete isotopic labeling of blue green algae (Spirulina platensis) with (15)N and utilizing it as a source of dietary nitrogen for mice. We outline a detailed protocol for in-house production of (15)N-labeled algae, labeling of mice, and analysis of isotope incorporation kinetics by mass spectrometry. The methodology can be adapted to analyze proteome dynamics in most murine tissues and may be particularly useful in the analysis of proteostatic disruptions in mouse models of disease.