Protein-tyrosine phosphatases (PTPs) have important roles in signaling, but relatively little is known about their function in vivo. We are using the zebrafish as a model to study the function of PTPs at the organismal, cellular and molecular level. The zebrafish is an excellent experimental model for the analysis of gene function. We have developed methods to quantitatively study effects of PTP knockdown or expression of (mutant) PTPs, particularly with respect to gastrulation cell movements. Moreover, we have studied the phosphoproteome of zebrafish embryos. In this review, we will discuss methods to manipulate the zebrafish genome and techniques that we have developed to assess developmental defects during gastrulation and to assess differences in the phosphoproteome.