Both opposing parties to a lawsuit are entitled to have the jury instructed as to their respective theories of the case where there is significant evidence relating to these issues. Denton v. Arnstein, 197 Or. 28, 250 P.2d 407 (1952); Cline v. Bush, 152 Or. 63, 52 P.2d 652 (1935); Holden v. Blitz-Weinhard, 45 Or. App. 83, 607 P.2d 776, rev den 289 Or. 275 (1980). Defendant was entitled to this instruction or its substantial equivalent to put before the jury its theory that plaintiff was not entitled to compensation for any portion of his disability which was due to plaintiff's earlier injury or disability.