The mRNA accumulation of phosphodiesterases PDE4D and PDE7A was studied by RNA blot analysis in human umbilical vein endothelial cells (HUVEC) incubated with TNF alpha for different periods. A contrasting behaviour was observed in the mRNA accumulation of the two genes. Further analysis by RT-PCR of the PDE4D and PDE7A splice variants gave different accumulation patterns which may indicate that differential splicing has a role in the regulation of these enzymes. Three previously undescribed PDE4D isoforms, with different accumulation patterns, were also detected. They code for truncated PDE4D isoforms, which could participate in the regulation of PDE4D activity.