The effects of dietary broccoli on the body's ability to detoxify were studied in 18 male subjects between the ages of 22-40 years. The biological parameters used for measuring detoxification were the four major urinary conjugates, namely, mercapturates, sulfoconjugates, glucuronides, and amino acid conjugates. Dietary broccoli increased the urinary excretion of mercapturates and sulfoconjugates, but did not influence the excretion of glucuronides and amino acid conjugates. A significant linear trend was observed over the six-day broccoli diet treatment for both urinary mercapturate (P<0.005) and sulfoconjugate (P<0.0001) excretion. The linear trend for the mercapturate excretion was in a dose-dependent manner, resulting in a 1.3 and 2.1 fold increase by the third and sixth days, respectively, of the broccoli diet, compared to the control. For sulfoconjugates, an unexpected decrease was observed on the first day of the broccoli diet. However, within the six-day broccoli dietary treatment, a continuous increase in conjugate excretion was observed, resulting in a 2.5 fold increase by the sixth day compared to the first day. The excretion of sulfoconjugates was not necessarily dose-dependent, and increased excretion at the highest level of broccoli (500 g) could be due to a time effect. Overall, sulfoconjugate excretion was the highest (3.98-8.91 mmole/24 h) followed by the amino acid conjugates (3.06-5.99 mmole/24 h) and glucuronides (2.85-3.54 mmole/24 h). Mercapturate excretion was the lowest (0.16-0.34 mmole/24 h). In spite of its low excretion level, the level of urinary mercapturates appeared to be the most responsive urinary conjugate to the different levels of broccoli diet.