Hydrolysis products of sinigrin (2-propenylglucosinolate) and glucoraphanin (4-methylsulphinylbutylglucosinolate) have been shown to protect against the development of cancers. However, there was limited information available on the variation of these two glucosinolates throughout the plant cycle. The objective of this study was to evaluate sinigrin and glucoraphanin levels within Brassica plants during development. Sinigrin concentration in B. juncea and B. nigra decreased from seedling to early flowering stage, increased in the late flowering stage and then decreased again during seed maturation. The lowest concentration of sinigrin occurred at the early flowering stage except in one genotype of B. juncea (PI 179858). Sinigrin concentration also increased in maturing seeds while the concentration in pods decreased. The concentration of glucoraphanin in B. oleracea var. italica decreased from the start of seed germination to the flowering stages. The lowest concentration was also found at the flowering stage. A higher concentration of glucoraphanin was detected in the green broccoli heads and flower heads than in other reproductive tissues. However, the highest content of glucoraphanin occurred at the green head stage and then declined as flowering was initiated. These results have shown that green and brown seeds of mustards contained the highest concentration of sinigrin while the highest concentration of glucoraphanin occurred in young broccoli seedlings and seeds. This information should be useful for the development of those compounds as nutraceuticals.