Alternative splicing of premessenger RNA is an important regulatory mechanism that increases the diversity of proteins transcribed from a single gene.This is particularly important in the testis because germ cell expansion and differentiation require many cellular changes and regulatory steps.To investigate novel developmentrelated alternative splicings in the human testis, complementary DNA microarray studies were conducted with the use of probes from human fetal testes,adult testes,and human spermatozoa.Of a total of 386 Unigene clusters found to be related to the development of the testis,67 clusters showed a total of 74 novel alternative spliceoforms. Developmental stage–dependent expression was also performed for a novel Unigene, NYD-SP20 (Hs.351068), which had 4 possible novel spliceoforms and another Unigene,CRISP2 (cysteine-rich secretory protein 2,Hs.2042),which had 3 possible novel spliceoforms.These results indicate that alternative splicing plays an important role in the complicated processes of testis development and spermatogenesis.