We are given two expressions:
\[
x^2 y^3 z \quad \text{and} \quad x^3 y z^2.
\]
Step 1: The highest common factor (HCF) is found by taking the lowest power of each common factor in both expressions. Since \( x, y, z \) are distinct prime numbers, we examine the powers of each factor in both expressions.
- For \( x \), the powers are \( 2 \) and \( 3 \), so the lowest power is \( x^2 \).
- For \( y \), the powers are \( 3 \) and \( 1 \), so the lowest power is \( y \).
- For \( z \), the powers are \( 1 \) and \( 2 \), so the lowest power is \( z \).
Step 2: Therefore, the HCF is:
\[
\text{HCF} = x^2 y z.
\]
Thus, the HCF of \( x^2 y^3 z \) and \( x^3 y z^2 \) is \( x^2 y z \).