Two trade-school companies agreed to combine.

Encino-based United Education & Software agreed in principle to buy National Technical Schools, an 80-year-old, employee-owned business in South-Central Los Angeles. The companies did not disclose the price. United Education, which operates 12 career schools in California, lost $2.9 million on revenue of $19.4 million in the fiscal year ended Jan. 31. Privately held National Technical, which has one school and offers correspondence courses internationally, does not disclose revenue or earnings.