Electronics company Samsung has admitted it gave a horse to the daughter of a woman who is at the centre of a corruption scandal embroiling the South Korean president.
Lawmakers were questioning leaders of big businesses in a rare TV hearing, as part of a huge corruption inquiry.
Eight firms admit donating funds linked to President Park Geun-hye, but deny seeking favours.
Parliament is due to vote on Friday on Ms Park's impeachment over the scandal.
Massive protests have been held in recent weeks demanding her resignation.
The executives are being questioned by a cross-party committee of lawmakers. The panel has no power to punish but its chairman has said the hearing is a place for apology.
The conglomerates are all accused of giving large donations to non-profit foundations operated by Choi Soon-sil, a close confidante of Ms Park. Ms Choi has been charged with coercion and attempted fraud.
Samsung has been accused of donating in exchange for support of a controversial merger that effectively strengthened the position of de-facto company head Lee Jae-yong.
The company gave a total of 20.4bn won (£16m; $17.46m) to the two foundations.
Prosecutors argued that Samsung paid $3m towards equestrian training for dressage competitor Chung Yoo-ra, the daughter of Ms Choi.
They say that Ms Chung spent some of the money on the horse, Vitani V, thought to be worth around $850,000.
Lee Jae-yong confirmed to the inquiry that the company had paid for the horse, saying he regretted doing this.
But he denied that money donated to the foundations had been given "in return for something".
Mr Lee apologised for Samsung's involvement in the scandal and said his company would "take all responsibility" if there were any.
One of the corporate bosses acknowledged that it was difficult for firms to say no to government requests.
"It's a South Korean reality that if there is a government request, it is difficult for companies to decline," said Huh Chang-soo, head of the GS Group and chairman of the Federation of Korean Industries lobby group.